first door: a person's belief system

What a person believes, what he think is possible or impossible, to greatextent
determines what he can or can not do.

It's true , for when you don't believe you can do something, you 're sending
your nervous system consistent message that limit or eliminate your ability to
produce that very result

If you are consistently delivering to your nervous system congruous messages
that say you can do something, then they signal your brain to produce the results
you desire, and opens up the possibility for it.