This is something I can't agree with. Capturing a school is a bad move, but not the worst – it doesn't lead to losing the game, at least not immediately. But Valeska standing behind a mountain is twice as bad.
Capturing the school for Gosha, who urgently needs to level up his armor, necromancy, and earth skills, and all this in the Shadow of Death, where 70% of the skills are useless, is a very negative move.
Moreover, the negativity is measured not in absolute terms, but in comparison with alternatives. Sometimes all decisions lead to defeat, but with different probabilities. The decision not to take the school here looks significantly better than taking it.