Learn Russian: В качестве командира он слишком требователен, чтобы простить эту ошибку. - As a commander, he is too demanding to forgive this mistake.

In English, we simply say "too demanding to forgive." In Russian, you can't just attach an infinitive. You must use слишком (too) + adjective, followed by a comma and чтобы + the infinitive (простить). This structure essentially translates to "too demanding, in order to forgive."

What does в качестве mean, and what case does it take?

В качестве is a fixed phrase meaning "in the capacity of" or simply "as." It always requires the genitive case, which is why командир (commander) becomes командира. It is a very natural B2-level alternative to using как when talking about someone's professional role or function.

Could I use the long-form adjective требовательный instead of the short-form требователен?

Yes, you could say он слишком требовательный, and it would mean the same thing. However, short-form adjectives are highly preferred in the predicate position (when describing the subject), especially in slightly formal contexts or when paired with degree modifiers like слишком or достаточно.

Why is the perfective verb простить used here rather than the imperfective прощать?