In Heroes of Might and Magic III your heroes gain skills as they level up. When you level up, you will be presented with two options for skills, one of which you can opt to learn. There are three tiers of each skill - Basic, Advanced and Expert.
Another way to gain skills is to get them from random dwellings on the map such as a Seer's Hut.
Because I don't look at what I'm doing and click anything that says unvisited, I always end up ruining my hero by learning a skill like "Scouting" or "Eagle Eye" from a random dwelling.
Is there a way I can discard these skills?