Either you have a tooltip explaining the function or you have to test it to understand what it does. But to test something you want to know it doesn't cause problems.

I feel like this is some fundamental UX dimension here. Cost and risk of learning. How much time do I have to use to learn all the commands or find the right command and if I have to try it what is the risk of breaking something?

Just as relevant in cli applications.

Another thing that helps is a predictable, reliable undo function. If the user believes that any action is easy to undo, unknown actions won't be so scary. Of course, this is sort of a chicken-and-egg problem, because other than ctrl-z in certain desktop environments (in which environments undo is not always either predictable or reliable), there is no well-known idiom for undo.

It's harder to damage things if tooltips give you some idea of what's going to happen when you push a button.