All performers, especially soloists, need to be aware of The Halo Effect. It has always been a struggle for me to maintain an air of confidence, especially when a performance is going less-than-stellar. This provides a psychological reason for why you should never let your body language or facial expression betray your inner fears, doubts, or regrets during a performance. People will enjoy a performance more if they are comfortable with what they are perceiving visually.
Matt Marks Music 