You’d be surprised to know that a big elephant can be held only a by a weak rope and the elephant will not make an effort to break away from its bonds.
When they are very young and much smaller, their trainer uses the same size rope to tie them and at that age, it’s enough to hold them. As they grow up, they are conditioned to believe they cannot break away. They believe the rope can still hold them, so they never try to break free.
These animals could, at any time break free from their bonds but because they believed they couldn’t, they were stuck right where they were.
Like elephants, we sometimes believe that we can’t be or get something that we want simply because we failed at it once before.