If something bad is forgivable, you can see how it happened and you can let it go without a long fight. We use it for slips, sharp words said when someone was tired, a mistake made under pressure. It keeps a human feeling: not only “the rules allow this,” but “a kind person could forgive this.” A small hurt is often forgivable; a planned betrayal is much less often called that. It is close to excusable, but forgivable still has a person in the picture — someone who might forgive. You will also meet unforgivable as the hard opposite.