1. Confidence and slickness of presentation, particularly in interviews, is usually inversely proportional to intelect and ability.
A confident person is often just bluffing or parotting. One who hesitates and stammers is thinking about what he says.
OK, yes it is a gross generalisation, but it’s closer to the truth than what many appear to believe. Too many people confuse lack of confidence with lack of capability, and too few have the expertise to see past nerves and lack of confidence to the ability beneath.