A person is going to believe what they want.

I agree, however,  that does not necessarily mean that their beliefs are truth. A persons truth, in order for it to be truth, would have to be based on facts, not just what they want to be true.
A man can believe that a certain female likes him. However,  when he asks her out on a date, and she refuses and says she would never date him,  the evidence states otherwise. The man can go believing she is just playing hard to get, however,  the facts show she is not interested, and in his "belief ", he is only deceiving himself.