Why is your own legacy so important?

Doesn't matter who you are or what you do, at some point in time, you will think about legacy. But who honestly believes that they have much influence in the first place or that people will even bother to remember them. People especially when they get older like in their sixties will think about this a lot. This is the one thing in life, they have absolutely no control over. Why agonise over something you can't control?