Friday, July 14, 2017

Software Engineering Maxim #10: Risk is multiplicative

(This is one of a series of Software Engineering Maxims Which May or May Not Be True, developed over the last few years of working at Google. Your mileage may vary. Use only as directed. Past performance is not a predictor of future results. Etc.)

There is a school of thought that when there are multiple large projects going on, and there is some relation between them, that they should be tied together and made dependent upon each other. The arguments for doing so are often:

  • "We’re going to pay careful attention to those projects, making them one project means we’ll be able to track them more effectively."
  • "There was going to be duplication of effort, we can share implementation of the common systems."
  • "We can better manage the team if we have more people available to be redirected to the pieces which need more help."

The trouble with this is that it glosses over the fundamental decision being made: nothing can ship until all of it ships. Combining risks makes a single, bigger risk out of the multiple smaller risks.