How do I give hard feedback without hurting someone's feelings?

Your reluctance comes from a good place. You do not want to cause pain, and that care is part of what makes people trust you. But withheld feedback is its own kind of harm. When you stay silent to spare someone, you often let them keep making a mistake that costs them more later. Kindness and honesty are not opposites. The truth, delivered with care, is a gift, not a wound. People can usually feel the difference between someone tearing them down and someone who wants them to do well. If your intent is to help, and you say it plainly and without cruelty, most people can take it, even if it stings for a moment. The sting fades. The help stays. Start small with one honest thing you have been holding back, said gently and directly to someone you trust. You are not hurting them by telling the truth. You would be failing them by leaving them in the dark to protect your own comfort.