the why's and others

I just hate it when I am about to make a decision that I am not even sure would work for the best. A lot has to be considered. Why is it that we can't make our decisions by just basing on our own happiness. Why do we have to consider other people's take on things that we get ourselves into? Why do we consider their happiness as well? Can we just do it for ourselves? Can we just be happy without having to worry about others? I know I have the answers to these questions. Then why do I have to ask them? Why?