Proverbs says an honest answer is like a kiss on the lips. That means it’s quite pleasant, right? But Job (who knows a thing or two about pain) says the opposite: Honest words are quite painful.
Is a kiss on the lips painful or unpleasant? It could be, depending on the circumstances. But when people think of a kiss, they don’t generally think of it as an unpleasant thing. So I don’t think that’s what the proverb meant.