Root canals are like any other dental procedures, once you are numb, it is like doing a filling, completely pain free. Also a reasonable percentage of infected root canals are done without any anesthesia at call with zero discomfort. Also using the rotary nickle titanium flexible files, root canals are done now more efficiently, and with a higher success rate.
A root canal is the last attempt to save a tooth from being extracted, that is why regular cleanings and check ups will help detect any cavity from getting to the nerve and ultimately causing the tooth to require a root canal treatment, or worse, extraction.