A mad, keen photographer needs to get out into the world and work and make mistakes.

Yes, there are billions more photographers, and billions more photographs every day, but who's building up a point of view? Who's photographing with intention, and whose body of work will sustain itself and survive?

Teaching has never been far from my life. It's the most natural thing I do. Apparently, as I said, I cannot not do it.

What I'm interested in is modern American history. I'm taken with the changes that have occurred in America in my lifetime.

The neatest part of this book I'm working on - to me - are the pictures that show the process... Because photographers... think things through and... it isn't luck, and it isn't random and it isn't accidental. It isn't.

I did a story for the Geographic on Meriwether Lewis and William Clark, and Stephen Ambrose was the writer. He said, "I've got the easiest job in the world. I just have to re-tell the story of the greatest fishing, camping, hunting, canoeing trip of all time. You, Sam, have the hardest job, which is, pretend like nothing has happened in the last 200 years.

I can't speak for other photographers, but the photographers who went forward strongly when the so-called "official" part of their career ended, to me, were those who had taught. Teaching enriches and enlivens one's work.