One thing I've noticed is that sometimes the crowd has an energy of it's own. Sometimes you just get a lot of people who are not interested in the music and want to talk and socialize (I'm talking pubs and restaurants here, not concerts) and sometimes everybody's interested in the music. There are some nights when it's easy to get everybody's attention, other nights when no matter how much I put into it the crowd's just not interested. I guess a real master can work any crowd, but I haven't reached that point yet!