If a person killed a deer and ate too much of it, he would feel sick and/or sluggish. Anyone who has overeaten knows that bloated feeling, especially after Thanksgiving dinner!
Truth is a good thing, just like deer meat is a good thing for a hungry person. But truth, too, has its negative side effects. When a person is exposed to too much truth, especially considering the age of the person, truth can hurt. Consider the breakup of a long relationship. When the truth is told, "I just don't love you any more", the one hearing the truth is hurt. When a child finds out why they were put up for adoption, they may feel rejection of a horrible kind. Adopted children may fantasize about a parent being too poor to care properly for them, and giving them up to a loving, caring couple. To hear, "I didn't want you" would make you as sick as if you have eaten the whole Thanksgiving turkey by yourself. Trying to continue living a normal life after that would take a lot of effort after that kind of rejection.