Came here to comment this. Most of the flakey tests are badly written, some warn you about bugs you don't yet understand.

Couple years ago I helped to bring a project back on track. They had a notoriously flakey part of test suite, turned out to be caused by a race condition. And a very puzzling case of occasional data corruption - also, turns out, caused by the same race condition.

I tend to find that those bugs are in the extreme minority.

Most flakiness ends up being a bug in the test or nondeterminism exhibited by the code which users dont actually care about.