In any given exchange, the speaker is likely optimizing both honesty and diplomacy, trading one against the other as the situation requires. The phrase "to be h

In any given exchange, the speaker is likely optimizing both honesty and diplomacy, trading one against the other as the situation requires. The phrase "to be honest" signals that the next bit is going to sacrifice an unusually large amount diplomacy for an unusually large amount of honesty. Or something. It's a verbal flag and a hedging move. "I am about to say something potentially hurtful, but I am doing it with your best interests at heart, so don't instinctively retaliate" is kind of what it's used for. Reading too deeply into the literal meaning of the words doesn't really go anywhere, any more than with other verbal rituals. Compare to the greeting "How's it going?", often used even when the asker doesn't really want to know how it is going.