Self-fulfilling Oxymoron

We say to those who feel sorry for themselves, are pessimistic, beat themselves up and THINK THEY CAN'T DO ANYTHING RIGHT to beware of "self fulfilling prophecy"...well isn't that an oxymoron?! If they feel they can't do anything right, then they certainly can't fulfill their own miserable destiny, right?! Apparently my prophetic moments and ephianies come in the shower...