Breakdown of Kiedy kolega robi błąd, musisz mu wybaczyć.
robić
to make, to do
kolega
the colleague (m) / the friend (m)
mu
to him
musieć
to have to
Questions & Answers about Kiedy kolega robi błąd, musisz mu wybaczyć.
Why do we use mu (him) instead of go here?
The verb wybaczyć (to forgive) requires the Dative case for the person you are forgiving. Because of this, we must use the Dative pronoun mu instead of the Accusative go (which you would normally use for a direct object).
Why doesn't the word błąd (mistake) change its ending after robi?
The verb robić (to make/do) requires the Accusative case for its object. However, błąd is a masculine inanimate noun. For masculine inanimate nouns, the Accusative form looks exactly the same as the basic Nominative dictionary form, so it doesn't get a new ending here.
Could I put mu at the very end of the sentence: "musisz wybaczyć mu"?
It sounds much better where it is. mu is a short pronoun, and in Polish, we avoid putting short pronouns at the very end of a sentence. Placing it between the modal verb (musisz) and the infinitive (wybaczyć) is the most natural word order. If you really needed to emphasize "him" at the end, you would use the long form jemu.
Does kolega always mean a work colleague?
Not necessarily! While it can mean a co-worker, kolega is a very common word for a "friend," "buddy," or "mate" (specifically a male one). It represents a casual friendship, as opposed to przyjaciel, which means a very close, deeply trusted friend.