Why do bad habits (chewing gum, toothpicks, tapping your fingers, etc.) increase your confidence?

This is not certainty. These actions (chewing, tapping, wiggling, etc.) help you enter a light trance. That is, to some extent relax - precisely due to the surface trance. You can still sort out the rosary)

But in general, this is perceived as a marker of excitement rather.

Usually, a person eats in a comfortable, safe environment, for tens to hundreds of thousands of years, a reverse reflex has formed - eating calms and relieves stress.

Chewing gum is analogous to eating - it does not increase confidence - it just calms: - ))))

A bad habit or a good role does not play here, especially since these are only our value judgments, objectively a habit or is it or not :-)))