Having doubt in one's own ability, merit, or judgement; lacking self-confidence; diffident.

What is self diffident?

Having doubt in one's own ability, merit, or judgement; lacking self-confidence; diffident.

What is a diffident person lacking?

The adjective diffident describes someone who is shy and lacking in self-confidence. If you are shy and have a diffident manner, you should probably not choose one of these professions: substitute teacher, stand-up comic, or lion-tamer.