Baracudas love mackeral. It's their favorite food.
Researchers once did a study in Florida in which they divided a large fish tank in half by putting a glass wall
in the middle. A barracuda was put on one side of the tank and a mackerel on the other. The hungry barracuda
tried to get the mackerel but smacked into the glass barrier again and again. The Baracuda, experiencing the futility of its attempts, gave up.
Researchers removed the glass wall and the barracuda made no new attempts to reach the mackerel. The
Baracuda
eventually starved to death even though food was within easy reach.
See Learned Helplessnes article.
The moral of the story, once walls are built -- even after removing the physical wall -- the walls in the mind remain even unto the end of days. death.