Sidewalks.

I wonder if there's a limit to the number of people you can get to know in a lifetime. If there's a limit to the amount of energy a person can expend exchanging and absorbing life stories. Perhaps if you share too much too often as a young person, you run yourself short on possibilities for new friendships later on in life. You can't keep hold of all those people you knew when you were ten or twenty or thirty, even though they represent a major investment of time and energy and intimacy of sorts. But it's difficult to replace them when you're young, and it's even more difficult when you're older. If you only have it in you to really, truly know twenty people in your lifetime, and you've met and parted with eighteen of those people before your fortieth birthday, you've only got two people left to draw newly close to you in the second half of your life. It's too bad you didn't realize until too late that you should have used your choices more carefully when you had the chance ten years ago.