The elephant and the rope 

While someone walking in the zoo, he stopped confused to realize that elephants retained only a thin rope tied to one of its front legs, without chains or cages. It was obvious that the elephants could break the rope that bound at any time but yet for some reason did not. A coach was approached for answers and was told: 

Well, when they are very young and much smaller we use the same size rope to tie them and, at that age, is more than enough to hold them. As we continued the coach-growing, still believe that they can not escape; believe that the rope still retains, so never try to break free. 

The person gasped. Elephants could be released from their bonds at any time but because they believed that they could not even try, and that was enough to keep them paralyzed. 

MORAL: Like the elephants, we usually strongly support the idea that we can not do something just because we have failed once or twice.