Why do root canals have such a bad reputation?

The vast majority of root canal procedures proceed painlessly, both during and after each visit!  With modern techniques and anesthetics people report that having a root canal treatment is about the same as having a cavity filled.  On the other hand, some people present with what we call a hot tooth.  A hot tooth is one in which the nerve is alive, but badly inflamed.  The tooth is generally already very painful, especially to hot or cold stimuli.  These are the ones that require multiple anesthetic injections to get numb.