I can't believe how much selfishness goes uncorrected in children. Yes, kids are selfish. They come into the world not caring about anything about their creature comforts: food, warmth, snuggles from mom and dad, and whatever else is handed to them to play with.
They learn early that "no honey, that's the baby's toy... give it back to them" when they cry gets them catered to. Somewhere along the line they grow into adults that expect to be catered to unless someone says "no, you most certainly WILL share that toy or I will take it away, because you will not be a selfish brat in my home."
Hello, Parents!!! The "someone" I'm referring to in that last sentence is YOU!!! They don't take a high school class on etiquette. They don't go to college to major in manners. That's YOUR job!!!
In my house, southern grace and hospitality rules. If I have pie or cake, it's for the guests first. My refrigerator is an open bar of milk and juice. Toys are community property when friends come to play. It's my way or it's nap time. Because I will not allow rudeness to rule in my home.
I wish more parents did the same thing. I get sick of hearing "but _____ doesn't share her/his toys when I'm at her/his house" whined to me. I get sick of saying "so sorry to hear that, but I'm not his/her parent, I can't make them share their toys in their home. In this home, however, you'll act like you have some manners until you actually have them."
Come on people. How hard is it to actually parent your child? Probably not nearly as hard as you'd like to claim it is right now... if you'd quit being so selfish.