Willis Harmon expresses it elegantly: we humans have an awesome ability to deceive ourselves, once we have settled on one perception of 'reality' all evidence to the contrary tends to become invisible. All hints or suggestions that our picture may be wrong or even seriously incomplete are warded off like flies on a summer's day".
A key task for the coach or mentor is to continually be alert to the client making assumptions about their reality and be willing to challenge those assumptions. For example - "Has there ever been a time when something you did worked?", "Who keeps letting you down?", "How did he reject you?", "What would happen if you did?", "How do you know?".
How we describe our experience to ourselves becomes our experience - if we say "I can't do that" then we probably wont. We have to take great care with what we say about ourselves and how we see ourselves because they have a habit of becoming true. As Henry Ford said "Whether you think you can or whether you think you can't - you are right!".