One, we live a cyclical life. Things naturally come and go into and out of our lives. It is simply the cycle of life. There often is no rhyme or reason to it. AT least it can seem that way to us. Life comes and goes, love comes and goes, friendship comes and goes. Sometime they come back around again, sometimes they don't.
The second thing is, and this is just my opinion, people and events come into and out of our lives to teach us things. God/Goddess/Spirit moves us to learn to grow. That doesn't happen with out things coming and going. Sometimes it's painful and sometimes it is absolute bliss.
I think one of the greatest lessons we can learn is, like the old saying, the only constant is change, the only permanent thing is impermanence.
I think you pretty much hit it on the nail there
I think one of the best things I have gotten from drudiry is peace with life's impermanence. Everything will come to and end and that is not a bad thing because there is no ending without a new begining. As Stephen said this is what nature reminds us of with each passing seadson. That feeling that winter will never end and then one day - like it came out of nothing - Snowdrops are coming up from under the snow.
Learning to deal with Impermanence can be more tricky and we cant really ignore it anymore. The days of spending all your worklife in one job is distant myth for most people these days...
I think there are 2 ways to deal with impermanence for me. The first is celebrating the change of the seasons, that way i always "see it coming" and all days I am reminded to treasure the here and now because tomorrow I will be of to other adventures. The second is to remember that I am always the eye of the hurricane that is my life. No matter how much everything changes tomorrow - I am always me - And that is permantent - for better or worse