And that is a bad, bad mistake. The result is often code that sort of worked, once, but is buggy and unmaintainable because nobody actually remembers what their assumptions were at the time it was written. They’re baked into code in cryptic ways, and trying to fix problems is terrifying because it’s so hard to tell when a change will break an undocumented assumption.

There is way to avoid this kind of mess. It’s to write down your assumptions before you write code, and treat that document as the authority of which the code is an implementation.