Your teacher asks who left the art cupboard unlocked, because expensive supplies went missing as a result. You know it was your favourite teaching assistant, Mr Cole — you saw him forget to lock it, and he's lovely, and he'd never mean to cause harm. If you tell the truth, kind Mr Cole gets in trouble. If you don't, the teacher might keep blaming the students. You like Mr Cole. The truth feels mean here, because it points at someone good who made an honest mistake. But the truth is still the truth, and right now a whole class is under suspicion for something one forgetful adult did. Telling it helps the students but hurts someone you care about. Both feel wrong in different ways.