Many people are not successful in many things they try to do because they have a closet pessimist mentality.
A closet pessimist is a private worrywart, someone who worries without letting others know.
These people put a brave face when they are in public but when they are alone, they worry themselves to death about the things they have assumed responsibility for.
This stops them from achieving their goals.
The consequences of being a closet pessimist are manifested in various ways, such as past failures, fears of facing the future, inability to own up to new responsibilities and so on.