It has to hurt, and it has to hurt bad. Why? Because you will not heed it otherwise. It has to sear your mind with white-hot pain so you cannot possibly forget what it says, and thereby induce you to do what it demands of you.
So, when I see fools--well-meaning or otherwise--talk about being truthful while not being hurtful, I see stupidity in action. Rather than spend a lot of space on detailed breakdowns on the hows and whys that won't be read, I shall summarize:
How many times have you disbelieved your elders' warnings, until the very thing they warned about happened to you or one of your peers? That's the truth talking, and it speaks via the language of pain. You don't forget it when it costs you something now, do you?
The Greeks called this "Nemesis", as this was divine punishment for hubris in mortals, and when Truth talks to you that's likely why.
You conform or it breaks you until you do.
So don't talk to me about being hurtful with the truth. You can just sit the fuck down, shut the fuck up, and piss right the fuck off.