Well, the truth is just about everything.
Who else is going to find my missing story on my computer and restore it to health (or at least to its pre-disappearance status)?
Who else is going to humor me by accompanying my wife, daughter, and me to Nationals games, even if we have to hold his eyes open with toothpicks?
Who else is going to know how to save us money by (a) replacing the lock on our front door himself, (b) fixing the window on our side door himself, and (c) doing a million other things around our house out of the goodness of his heart?
Who else is going to drive out to the batting cages at Rocky Gorge with me, so that I can have company when I practice my swings, and in doing so prove to me that he can hit the balls farther and more often than I can?
Who is else is going to make my daugther as happy as she can be?
The answer to all of the questions above is: no one.