It's weird, the people you develop long-lasting relationships with. Of the people I'm friends with now, well... I wouldn't have guessed. I won't mention any names, but there are certainly those who I assumed I would have a school-friendship with, and yet it mounted into something huge. And then of course there are those that I met and clicked with and thought, "this will be forever" and then it ended up being short-lived, for whatever reason that I don't know.
So what? What is it that enables two people to form an unbreakable bond? It's not having many things in common. It's not seeing eachother often. Maybe it deals with having one passion in common that you can both relate to. Maybe its purely "getting along" -- but then what causes that? I get along with many people that I've never developed a friendship with, and it bugs me that I don't know why I chose certain people to become friends with, or why they chose me.
Ever notice how you have some people that you can just to for hours and others who you just can't? Even if the conversation relates none to their life, and is all discussion of ideas and topics that you bring up. You have the same things to say, but you just can't think of them, or don't want to, when you talk to those who don't connect in the same way.
Or maybe you have the exact same experiences with people. Perhaps even a group of people? Is it voluntary that you choose one out of the group to be better friends with? Is it based on geography (whether it be living close to one another, or even micro=geography where you happen to be standing next to one another)? Is it some sort of pheremonal thing?
Can a person crawl their way back into your life even if you don't want them there, and become a lasting fixture? (Think Phoebe cutting Monica out, but Monica getting back in 'cause she's scrappy). It's happened before that a person will work hard to hang out with me even if I don't particularly want to see them... and now I'm so glad they did, that they worked their way into my life. Do I do that to other people?
Friendship is a two-way street, but there are times in every friendship where you come to a fork. If you keep calling them and wanting to hang out, you continue to be friends... but if you slack, the mutual lack of care becomes a mutual decision to let the friendship go. Sometimes you have to know that the other person needs you as much as you need them. But say the other person doesn't ever call you, or make plans to hang out.. but one person does, and they still hang out and the person who DOES the calling has a good time. We don't know the feelings of the second person. Does the second person just rely on the first to be the initiator? Does the second person not care to see the first person at all? What would happen to this "friendship" if the first person were to quit calling? And what would happen to the two friends, without this other friend in their life?