What is it that makes a person self-aware?
Well, science narrowed it down to the brain some time ago, and has by a process of elimination excluded quite a lot of the brain from being a seat of self-awareness. I'm not up on the latest research, but I seem to recall that there were a few substructures in the brain that are candidates, and laboratory tests are underway.
I cannot prove that there are no psychic powers, any more than you can prove that there is not an invisible dragon in my garage. That's a straw man. But a person of science will not believe that something exists without repeatable evidence.
And don't even bother with that "understanding how it works" crap. Many great insights start with unexplained observations. The key is that the observations must be REPEATABLE. In lieu of repeatable observations, psychic friends substitute handwaving and anecdotes. Any rational being should be ashamed to be associated with such frippery.