Some "clean" UI is just hidden UI

Clean" means two things: less visual noise, and less mental effort. They fight more than we admit.

I've shipped flows that looked great stripped down, then watched people stall in testing. The button that blended in was cleaner and invisible. The minimal form was elegant to me because I'd already learned it. First timers met it cold.

We judge our work after memorizing it. Users meet it at first contact.

Where's your line? When should minimalism step aside and just tell people what to do?