Some people examine Step Eight and come to the conclusion that the only harm they have ever done someone is to drink, that, otherwise, they have never done anything wrong.
Unless one is the Second Coming, this is simply not true.
For a basic understanding of harm, see this article:
To identify more substantively whether one has harmed someone, one can use a good list of character defects, pausing to consider whether, during the course of one's life, one has ever taken the action described; if so, there is harm.
(If one objects to the overtly Christian 'sins', one can skip over those. I'm sure sufficient others will apply for the exercise not to be wasted).
Lastly, one can go through the chapter on Step Eight in the book Twelve Steps and Twelve Traditions, pausing to reflect on each type of harm described, and asking oneself, again, if one has ever taken the action described; if so, there is harm.