"Negative feedback is like a police force. A nosy, strong, and merciless police force is desirable and necessary when you live in a crime-ridden city; whereas surveillance, 44 magnums, and tough-guy attitudes are unwanted and unneeded when you live in an honest, respectful, and peace-loving hamlet. Tubes just happen to be such good audio citizens (because they hold their own internal feedback mechanism) that we seldom need to hammer and twist their output into line in a heavy-handed manner."