I was out drinking one night many years ago right around the time mullet spotting became a meme. Several beers into the evening I spotted a college age kid walking into the bar sporting a classic example of the tennis mullet. Being a service minded individual (not to mention very drunk) I marched over to him and asked him if he was aware he had a mullet and directed him to http://www.mulletsgalore.com/ the next time he was near a computer. The kid looked at me like I was nuts but he wrote the URL down. Mission accomplished I went back to drinking with friends.
A month later at the same bar I was approached by a vaguely familiar dude with a sharp looking haircut. He introduced himself, thanked me profusely for telling him about mullets and bought me a round before joining up with the rest of his friends. Apparently the kid just hadn't heard of mullets yet and I'd done him a real service by bringing him up to speed on the subject.
However, if that solution takes time to be alleviated, such as being grossly overweight, ugly or simply stupid, these kinds of "honest truths" will cause true harm because they will cause strong self-esteem hits that will linger over time. I for one would be happy and want with these kind of "temporary hurtful truths" told to me. I would like to say I would be the same for the long-term ones, but I'm sure I would be truly hurt just the same.
Seriously, the idea that I could have just not realised I'm fat baffles me.
Clip from white chicks about that (opposite of a fat person thinking they are not, but similar principal I guess): http://www.youtube.com/watch?v=6Gy4xMgArmk (dressing room scene -- possibly NSFW)