Harmonic playing is based upon feeling, particularly in light of its connection to folk traditions such as blues. The latter, based upon a modified scale, the blues scale, is particularly known for its expressive qualities. The typical blues "harp" playing method is cross harp, giving a flatted seventh scale tone which is inherently expressive. Even song titles express this, such as "Blues with a Feeling".
Sonny Boy Williamson, one of the most influential blues harp players, often expressed his performer attitude in his lyrics, which expressed themes like "get yo' hand out of my pocket" and even lapsed into a threatening mode at times. Note for instance the song title, "Your Funeral and My Trial". According to blues drummer Rod Rolle, who plays in the award winning Stiff Pickle Orchestra, "blues joints back then were rough places", which might explain the tough philosophical stance expressed by Williamson.
Other harmonica players from other traditions of course would not share Sonny Boy's tough demeanor. Bob Dylan pioneered electric folk, but his harmonica work was mostly straight harp and was integrated with a more sanguine assessment of human nature. Magic Dick, player in the legendary J.Geils Band, may straddle these two extremes with the hard partying songs and harmonica playing of the seventies.