Most root canals aren't painful in themselves, it's the injection of anaesthetic (novocaine or whatever) and the soreness in jaw muscles from having one's mouth propped open to an unusual degree for hours on end that usually bothered me afterward.
They are annoying, but you have to admire the person who knows enough to do one competently. They take years of training. I have often wondered what motivates people to go into dentistry. It seems an odd calling.