Now when most people think of proof, they are usually talking about reason or evidence, or some combination of both.
But there is another way we can talk about proof that would really only make sense to psychology.
It can happen that some combination of experience and beliefs has made it so that a mind simply cannot change about a particular thing.
When this has happened, we can say something is proven to a mind.
The concept of a phobia, would illustrate this notion of proof in psychology. For example, with the fear of water, some combination of beliefs weathered by experience has made it apparently impossible for the individual to see the world any other way. So that they cannot not fear water.