Truly? I think it stems from our infancy. I was just talking to DH about this last night. As a parent, when you have a baby who is crying and can't express their needs any other way, you look for the obvious: dirty diaper, needing attention and hunger. If nothing helps the wee one to stop their fussing, we feed them (and I'm not saying this is a bad thing! After all, we want to take as good of care of our babies as possible.) I think for the most part if they don't want the food they will refuse it, but how many times do we feed them when that's not really what they want? We learn at a very early age that food is one of the most comforting things in the world. It's something we need to unlearn as we mature.