Secondary skills in Heroes 3.

Smok, I recommend paying attention to the section title.

I still remember one case.
My son and I played in an alliance against a bunch of AI opponents. The AI had a lot of castles, about 4 of them were Titanic-level. Plus, they had the Grail.
Well, we took one of these castles. Of course, the AI came to attack. The army was 8 times stronger (at least), and the hero was powerful.
But! There were two nuances:
1. The AI had giants, not titans.
2. The AI hero was leveled up, but DIDN'T HAVE THE BALLISTICS SKILL!!!

What happened next? I don't need to tell you.
So, everyone probably understands now.
In three turns, we destroyed the catapult, and the AI, with its giants, retreated!