India, June 20 -- It's strange how much we change without realising it, and how the absence of such change in another can suddenly bring home the difference.

I have a friend, Ricky, who I have known for decades. He was the source of the rock 'n' roll CDs that defined our youth. It was from him I learned to headbang. We spent hours listening to Sweet Child O' Mine and Patience by Guns N' Roses. "Now that's a love ballad," we used to say. We lived for music. He continues to. I've changed.

Let me illustrate. Last week, I heard he had gone to Berlin, and assumed it was on a work trip. It turned out he had travelled there to watch Metallica play what may be their last live concert.

When I heard this, it was like a juke box was switched on i...