On AskMe, someone posted about their struggle to find meaning in life after deciding that atheism was for them_
I realize that, without "something behind everything", it doesn't matter one iota (speaking from a selfish perspective here) whether I build great things or just sit on my couch and rot, whether I live to be 100 or die tomorrow. It will matter to some, but not to many, and not for long.
I decided to respond_
Surely, you've known someone who has changed your life immeasurably for the better. This may be your parents, the guy who pulled you from that burning car, or the teacher who encouranged you to make use of your talents. I bet you wouldn't say that their contribution meant nothing.
I promise that I'm not getting all hippie on you here, but both the love and hate you express tends to propagate through society, starting with the people you interact with every day. No, really - there has been behavioral research showing that this phenomenon exists.
Furthermore, your life choices, like quitting smoking, or losing weight make it more more likely that your peers will do the same.
As James Fowler puts it (as quoted in the above link):
"Everyone always tells me that this research is so depressing and that it means we don't have free will. But I think they're forgetting to look at the flipside. Because of social networks, your actions aren't just having an impact on what you do, or on what your friends do, but on thousands of other people too. So if I go home and I make an effort to be in a good mood, I'm not just making my wife happy, or my children happy. I'm also making the friends of my children happy. My choices have a ripple effect."
Now go out and start some ripples.