How large an advantage is confidence (not arrogance). Will "I know I can" always yield better results than "I think I can"? How?

People view that word in all kinds of contexts.

Overly-confident denotes foolhardiness.

No confidence inspires one to flee.

I think having courage of convictions and the ability to discern when to act is the major attribute of confidence when used in the right venue.

I can be confident.  That doesn't mean I know my butt from a hole in the ground.  So, it depends on who it is and what kind of brain matter is involved in the process.