You can understand lots of things without being to explain them. It's called instinct, sometimes, taste, other times, experience by yet others.
Do you think the experienced cook can necessarily explain exactly why some things work and others don't?
Similarly if the UX designer says "this label should go here" he should be able to explain why: "the form is easier to understand that way". And if the client doesn't see why it is easier to understand he should be able to make two versions, and the client should be able to see why one of them is better. If the client cannot see that and the UX designer cannot convince him then it probably isn't better.
I've had cases where the person I'm working with can clearly explain why he feels one UI is better. And I was just as adamant about a different UI. I coded both up ways up, we played with both -- and we were still on opposite sides of the fence.
In this particular case, we ended up throwing both our solutions out the window and found something better, that we both agreed on. Unfortunately, it doesn't work out that easily.
Do you think the experienced cook can necessarily explain exactly why some things work and others don't?
They should be able to!
It's not magic - there are well accepted rules for what works and what doesn't. If they can't explain them then they are probably just following a recipe very well. That's fine, and may make great food, but creativity takes understanding, and understanding means they can explain what is occurring (at least to themselves).
None of those are 'understanding'.
> Do you think the experienced cook can necessarily explain exactly why some things work and others don't?
No, which means he doesn't understand what he's doing, merely that he's built up empirical knowledge about what works and what doesn't.
He can teach that knowledge to someone else but that's just transferring the 'ritual', not the underlying knowledge.
Don't underestimate all of the cooks though, some of them are quite knowledgeable when it comes to the underlying chemistry and the theories of taste and smell.
I very much agree you don't really understand something you can't explain.
It sounds to me like you want this to be a 'one way street' because you trump others in your superior knowledge of design. But the reality is that everybody - also non designers - will have to feel good and be on board about the stuff they build. So you'll have to do a better job at getting them on board with less effort. And if that can't be done wanting people to 'shut up and just do the job' isn't going to go very far.