Don’t mix jobs

by Jason Swett,

Many programmers spend most of their working time in a very wasteful manner.

One of the biggest sources of waste is the mistake of mixing jobs. In this post I’ll explain what I mean by mixing jobs, why it’s bad, and how to avoid it.

Mixing the “what” with the “how”

When you write a line of code, you’re actually carrying out two jobs. One job is to decide what you want the line of code to do. The other job is to figure out the exact syntax to accomplish your goal. You could call these two jobs “what to do” and “how to do it”.

Mixing a “main job” with a “side job”

Another form of mixing jobs is to start working on a certain job, then notice some semi-relevant problem or opportunity along the way, and immediately start addressing the new job in a way that’s not separate from the original job.

Why mixing jobs is bad

Almost everything we do in programming is to accommodate the fact that human brains are weak and frail in the face of the staggeringly complex task of building and maintaining software systems. If humans were infinitely smart, we could just write everything in assembly code directly on production servers. But we aren’t, so we need accommodations.

One of these accommodations is to carry out our work serially. It’s much easier to work on exactly one thing at a time, and bring it fully to completion before starting the next task, than to juggle multiple tasks at once.

Working serially might intuitively seem slower. It feels like it would be more efficient to batch things up. But humans are so susceptible to mistakes and oversights and confusions and such, and software systems are so complicated, that batching work costs more time than it saves.

Tips for not mixing jobs

When you’re working on something, always be conscious of the answer to the question “What job am I working on right now? What exactly am I trying to accomplish?” Once you’ve determined that, ask yourself, “Is this actually just one job or are there multiple jobs inside it?” If it makes sense, separate the “what” jobs from the “how” jobs.

It may take some experimentation to find the right granularity. I wouldn’t advocate planning the entire “what” for a program (e.g. writing out the whole thing in pseudocode) before starting any of the “how”. I personally like to decide a few steps’ worth of “what”, then figure out the “how”, then switch back to “what”, and repeat.

Avoiding mixing a main job with a side job is conceptually pretty easy, although it might take some discipline. When you’re working on a job and you notice some other job that needs doing, don’t just switch focus and do that other job. Instead, make a note to do that other job. I personally like to keep a daily to-do list where I keep track of such things. Before the day ends I’ll usually either complete those “side jobs” or, if the side jobs are big enough, I’ll capture them in a way that they can be remembered for later when they can be given the level of care and attention that they call for.


  • Don’t mix the “what” with the “how”.
  • Don’t mix a “main job” with a “side job”.
  • It’s generally faster to carry out work serially than to try to do it in batches or in parallel.

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