These people tend to see failure as a hurdle, rather than seeing it as a building block towards success.
This may stem from an inferiority complex, or a low self-esteem, that remain unattended from an early age, and could not be diagnosed.
On the other hand, when he gives his optimistic son a room full of horse dung, he sees him digging through the manure using a shovel. Out of curiosity, the father asks him what he was doing. The son replies, "since there is so much horse manure, there's gotta be a horse in there somewhere."