Your friends are extensions of you.
So there is simply too much wonderful stuff to do in life, and not enough me to do it. That is why I have started internalizing the accomplishments of my friends. I have found, with two cases in particular, that on seeing the exciting accomplishments of friends, my own longing and sense of unfulfillment to do whatever they did decreases. Two examples:
I've read a bit and been curious about California Central Valley migrant labor life. My friend Ghe was looking into someway to do premed work outside the making-money-off-of-premeds industry. After a good brainstorm, he is planning to go deep into California and see how he can help. And now, strangely, I can internalize his accomplishments and feel like I don't need to do anything like that. Almost like 'it's taken care of'.
Second. I was a late bloomer to computer culture and would love to have learned to cause a little trouble and get into the deep deep underbelly of how nets work. But, even though it's never too late to do anything, I feel like it is probably awfully late. But now that I have hooked my 11 year old brother in the Philippines with a Linux laptop and lots of tutorials, I feel like I can raise hell vicariously through his own significantly less regulated exploits.
You can't do it all, unless you do it all through your friends. It is a great alternative to being jealous about their accomplishments (admit it happens) and you get a lot more done. I have to admit that there both of these examples have a trait which makes it much easier to identify with the accomplishment. In both cases I planted the seed and passed it on. I can see that it gets harder to feel a part of other's accomplishments the more indirect your influence over it. But if you are going to live a life of air ball self delusions, you may as well pick exciting ones. Why stop at friends? Imagine taking everything that happens as your fault/accomplishment. Maybe it isn't true, but it is more true than its opposite.