I believe the greatest and most important thing in the world is a smile. They are what really make things in life all the worthwhile.I mean, what would be the point of living if there was nothing that could make somone smile. It's really what gives people good feelings when they do a good deed. Also, when a person smiles at somone, the other person smiles back. It'a what makes a greeting a greeting and is the only thing that can be used to express joy. Happiness wouldn't be happiness if there wasn't such thing as a smile.