In my experience, my root canal was a little uncomfortable until it healed, and then there was no pain. I've been told by several people, that even with a good root canal, and crown put in by a good dentist, you can expect trouble with it shortly after the 5 year mark. I'm not saying there are not exceptions to that, but that seems to be the general consensus among family, and friends that have had it done. Twice through the years, I've gotten a cavity under a filling. I suspect the material used for the fillings tends to prevent them from seeing a small cavity on x-ray, otherwise they would have picked up on the cavities under my fillings much sooner.
Daughter 1 almost never brushed her teeth. Daughter 2 brushed her teeth faithfully. Daughter 1 would get some Barkeeper's Friend, (I was not aware of this at the time) and scour her teeth a little before going to the dentist, and he would comment on how clean her teeth were, and she never had any cavities. Daughter 2 would get cavities, and the dentist would scold her, and tell her she should brush her teeth, like her older sister, and she wouldn't get cavities. It would infuriate daughter 2. This continued for years, until they were both in their early 20's. Daughter 1 started having problems with her mouth. When she whined about it, Daughter 2 laughed, and said "All these years, I've brushed faithfully, had my teeth cleaned twice a year, and had to endure the dentist scolding me for not brushing and keeping my teeth clean like you, while you never brushed, so I don't want to hear it, and I hope all your stupid teeth fall out!" Daughter 2 has not had any dental problems since childhood.