Negative Childhood Conditioning
This is all the negative BS you were told as a child by parents, teachers and peers. Things like 'You're not good enough to play on that team, you'll never amount to anything, you're lazy, dumb, fat etc.
When this happens often enough, or you get bullied, very soon your child-like mind takes on these beliefs and make it your reality. Soon enough you honestly believe that you simply aren't good enough, that you're different to the people you admire or that what you really desire in life- be it a loving family environment, to be on the same financial level as your friends and to be accepted or loved unconditionally simply isn't available to you.
Soon, believing that certain opportunities are just not meant for you, you stop trying and switch from thriving into surviving mode.