Technical debt is not a thing

In software engineering, we have this concept called “technical debt.”

When we talk about technical debt, we usually mean that, because of a given technical decision, we’ll be making “interest payments” out of our productivity until the original “debt” is paid off. These payments can take many forms, from manual toil to risk to cognitive load. Anything that saps our productivity on a recurring basis.

Technical debt is a metaphor. It’s a conceptual tool we use to grapple with elusive, abstract stuff like productivity and value. That abstract stuff gets grounded to a more concrete family of concepts: namely, money and debt.

All of which is well and good, if the metaphor helps us reason. But it doesn’t. The technical debt metaphor serves only to obscure and encumber. We must discard it.

Direct and indirect work

We use the technical debt metaphor when we’re talking about strategy: our plan for undertaking certain pieces of work in a certain order so as to achieve some goal.

The most straightforward kind of strategy for a software engineering team would be to do nothing but build high-value features. Pick the highest-value feature that can be built in a sprint, build, repeat. Get paychecks, win promotions.

This strategy works for some teams. But for most, it’s naïve. If we only do direct work (what I’m calling, more-or-less, feature work: work that creates value for customers), problems start to emerge. We find ourselves repeating manual procedures, fixing more user-facing bugs, and fighting more fires. All this unplanned work demands our labor, diverting it from direct work. It thereby reduces the effective rate at which we can create value: our team’s capacity (“velocity”, if you Agile).

In order to keep our capacity from slipping, we have to do indirect work. Examples of indirect work are many and varied: writing internal documentation, caring for test suites and CI pipelines, building metric dashboards, refactoring old crufty code.

Indirect work uses some of our capacity. But we hope that, by folding indirect work into our strategy, we can avoid a lot of disruptive and expensive unplanned work that would otherwise emerge.

However, on its own, indirect work doesn’t tend to float to the top of the priority list. We usually prioritize tasks based on how much value they directly create for customers. It’s hard to even talk about direct and indirect work in the same conversation. It feels as though they create forms of value that are incommensurable: impossible to prioritize with respect to each other according to a single metric. Therefore, direct work tends to elbow indirect work out of the roadmap.

Nevertheless, we know from experience what happens when we neglect to do enough indirect work. Everything falls apart and we fail.

How we use the technical debt metaphor

The metaphor of technical debt is mainly a tool for working around the incommensurability of direct and indirect work. It’s how we try to balance tasks whose output is an amount of value (direct work) and tasks whose output is an increase in the rate at which we can create value (indirect work).

“Rapid progress isn’t free,” we say to management. “It’s achieved by taking out a sort of loan. We get to ship sooner, but in exchange we take on an obligation to make recurring payments, in the currency of labor.” These recurring payments only touch the interest. They will never, on their own, pay down the principal. To do that, we need to undertake some more substantial effort. A “paydown” project that will liberate us from the waste – the toil, or risk, or cognitive load – that our technical debt entails.

The technical debt metaphor feels true. And it carries some useful baggage from its origins in finance to its new home in software engineering. Namely: neglecting your debts is short-sighted and irresponsible. Almost everybody agrees on this, at least with respect to real debt. So, if the metaphor holds, why shouldn’t it be true of tech debt too?

Thanks to the implicit association between paying down debts and responsibility, engineers and management both get what they want. Engineers get to spend time doing work that benefits them directly. In other words, they get a respite from the feeling of alienation from their labor product. Management gets a plausible justification for prioritizing work that keeps their team happy. It’s a win-win, right?

How the metaphor fails us

If you take out a real loan, your payments are usually proportional to the initial principal. It’s a rough proportionality, since interest rates and maturity dates vary, but in general: the bigger the loan, the higher the payments. Mortgage payments are higher than car payments.

This fact about loans has an important implication. Since the labor you have to expend to pay off a loan is (roughly) proportional to the amount of your recurring payment, loans are always worth paying off. If you have a tiny loan, it will take a tiny amount of labor to pay off, so it’s worth doing even though the interest payments are tiny. If you have a huge loan, then your interest payments constitute a significant financial drain, which makes the loan worth paying off even though it will take a lot of labor to do it. So we all share an intuition about loans: there’s no responsible alternative to paying them off.

This intuition implicitly tags along with the debt metaphor, because of how metaphor works, into the engineering space. We feel we must pay off our debts. But since technical debt paydown tasks never seem to make it onto the roadmap by themselves, we have to come up with some system to force them into the pipeline. To spend a certain proportion of our labor paying down technical debt, even though we won’t have any new features to show for it.

The number cited most often is 20%. 20% of our time feels like about how much it takes to pay down the right amount of tech debt. So we throw all the tech debt into a big bucket and try to devote about 20% of our labor to tasks in that bucket. After all, it’s debt: we can’t just not pay it.

But the dynamics of technical debt are quite different from those of real debt. Different enough that this intuition no longer stands up to reality.

How much are we paying in interest?

Imagine, for example, that a team decides to forgo automating a software product’s release process. By accepting a manual release process instead, they’re able to launch a week earlier than otherwise. But, since they lack an automated release process, they need to do an extra t hours of work each month.

The decision to accept a manual release process in order to launch earlier could be classified as taking on technical debt. Which means, if we apply our intuition about real debts, that it must be paid off. So it will go into the “tech debt” bucket and get done as part of the team’s 20% time. Regardless of the value of t. In fact, on most teams (in my experience), t isn’t even discussed. The task is qualitatively tech debt, so it goes in the bucket.

But you have to know t. If t is high enough, then there’s an enormous drain on our productivity which must be rectified urgently. If t is low enough, the task might not even be worth doing at all.

How much will it cost to pay down the principal?

Furthermore, in order to know whether it’s worth paying down a given bit of technical debt, we need to know how much it will cost to pay down.

Going back to the example from above: suppose it will take P hours of labor to automate the release process. If P is low enough, the automation is worth building. But if P is very high, it’s better to accept the toil and move on.

P doesn’t tend to be discussed either. Or, rather, first we decide that something is technical debt, and only when it comes time to prioritize it with respect to the other technical debt in the bucket do we ask about P.

Rejecting the technical debt metaphor

So, in order to strategize – to decide what work to do in what order – we need to estimate, at the very least:

  • t: The amount of value that will be created by doing a given task
  • P: The amount of labor required to do the task

Fine. But are these parameters not both necessary for evaluating feature work too? And if we need to consider them anyway, regardless of whether a task is technical debt, then what’s the point of calling some tasks technical debt paydown and others not?

The defining characteristic of technical debt is the decision to sacrifice some amount of future productivity in exchange for earlier delivery. But this decision is not unique to technical debt: it’s universal to engineering. Every change we ship – whether for a feature, or a bug, or a technical debt payment – every change carries an implicit decision about how much value to defer and how much to deliver now. “Technical debt” is just what we call it when the deferred value takes the form of a decrease in our team’s velocity. But that form doesn’t make it special or different, or incommensurable with other work.

When we make strategic decisions – decisions about what work to do in what order – we need a guiding principle. “Spend at least 20% of our time paying down tech debt” is not a principle. It’s an excuse to substitute our arbitrary personal taste for a realistic, evidence-based appraisal of cost and value.

And yet, something must be done.

But okay: so what if the technical debt discourse is useless? We’re dissatisfied with how much time we lose to recurring low-value-add tasks. Without the technical debt metaphor, how can we make the case that it’s worth investing time to eliminate these drains on our productivity?

One way is to adopt the simple model of a time horizon. Suppose a team declares the following as their goal:

To produce the most value possible over the coming year.

This team has a time horizon of 1 year. So, when there comes a proposal to make a particular improvement to their productivity (be it a process fix or some automation or whatever else), they can estimate:

  • How many hours of labor it will take to implement
  • How many weeks it will take to complete that labor
  • How many hours of labor it will save them over the year (the remainder of the year, that is, after subtracting the weeks spent implementing)

In this way, productivity investments can be evaluated each on their own merit, rather than being lumped together into the “technical debt” pile. The investments with the highest expected returns will emerge as clear priorities. And many proposals can be rejected entirely, if it’s determined that they require more labor than they can possibly save over a year.

With an agreed-upon time horizon, direct work and indirect work become commensurable. We get a more coherent strategy, and we don’t waste time wringing our hands over what’s technical debt and what’s not. The technical debt metaphor falls away, obsolete.