Why is it that every beginning has to come with an ending?

So I have been roofing and siding for over a decade now. I have been doing one form of construction since I was sixteen years old and in three days I will be done with it. Now most twenty six year olds have not been doing one job for over a third of their lives, but I have. It is a strange feeling to me that I only have two more days left of getting up on a roof or setting up a ladder first thing in the morning. From now on I am going to have to fire up my computer instead of an air compressor. I am going to have to set up sales pitches instead of nail guns and most importantly I am going to be working with a bunch of strangers instead of some of my best friends in the world. I have finally taken that first step into a much larger world, I am just hoping that when I finally get there, I like it. So with that, I will bid my old job a bittersweet farewell and hope the new job welcomes me with open arms instead of a swift kick to the balls. In closing, I will just say this: Why is it that every beginning has to come with an ending?