If your toilet overflows when you push the lever down and flushes when you pull the lever up, you'll learn pretty quickly how to use it. And other users will too, after they screw up or after you carefully explain so they're sure to understand. But it's just a shitty design! The fact that you've learned to deal with it doesn't excuse it or mean it shouldn't be fixed for all future users.
I want to get it right the first time; I don't expect to only because I've been hurt too many times by shoddy UIs. A good UI, whether a GUI, API, CLI, or other TLA, guides users through their workflow as effortlessly as possible by means of sensible defaults, law of least surprise, and progressive reveal of power features.
Relevant http://xkcd.com/1168