Getting by with little help

Friends. I spend a great deal of time wondering how much effort should be put into rejuvenating flagging friendships. It is true that friends are around for a reason, drifting away when the reason is fulfilled, whatever that reason may be? When you lose touch with a friend, how much time do you spend chasing before it's time to resign yourself to the fact that they may not need you...or want you in their lives? Do we accept that friends come and go...or do we remember why we were friends to begin with and focus on that as a reason to keeping trying to reach out? I wish I knew.