The word “I” tends to be used by less confident people for the following reasons:
1. The royal “we” used by royalty and some others who consider themselves royal, though royalty uses it less nowadays.
2. People with overblown egos tend to imagine themselves as representing the world, so they say “we” meaning “I and the less significant beings who inhabit this planet and surely agree with what I say because I’m right”.
3. People who have friends and family actually use the word “I” less because they are with other people. They also tend to be more confident.