Then how do the wizards build new buttons?I see it like the button next to an elevator. You push the button and sometimes the doors open right away, and sometimes you have to wait for the doors to open (also sometimes the doors open even when you don't push the button). Maybe the doors normally open faster between the hours of 2 and 4pm and slower at 9 am, 12 and 5 pm, but could be slow during those times too.
With that set of information, what do you "know" about how the button and the elevator doors work?
I can think of wizards as operating with this level of understanding. They know that if they press the button something will happen eventually but also that unexpected results may occur (e.g the door opening without pressing the button). Maybe they develop schedules to try and optimize the fastest result, maybe those work consistently, maybe they don't.
Because wizards can make spells. Not just cast them, they can invent new spells.