Some years ago, I got to know a high school football coach in Georgia. I was writing a newspaper column then, and he coached in a small town on the outskirts of our coverage area. But I was drawn to him — he was entertaining, and his teams were good, and if there’s one thing we columnists love, it is sure-thing columns. And he was a sure thing. I drove out to see him many times, went to dinner with him more than once. We talked on the phone often — he was funny and happy and thoughtful and all those good things. I probably wrote 10 columns about him over the years. I figured I knew him.

So when he committed suicide, I asked myself again and again how I could have missed it.

I came to the conclusion then — a conclusion that has congealed through the years — that people are complicated and contradictory and mysterious and often bewildering. Good people do bad things, bad people do good things, happy people get lost, lost people become heroes. This is the wonderful and depressing and daunting challenge of writing about people. Things don’t always make sense. Mistakes are made. Greatness emerges when you don’t expect it. There have been thousands of books written about Abraham Lincoln. There will be thousands more. And none of them will ever get him in his entirety.

A few months ago, I began working on a book about Penn State coach Joe Paterno. I have spent the last few months living in State College, Pa. Paterno gave me permission to write the book, but plays no editorial role in it. I decided to write about Paterno for a hundred reasons, but mostly because I’m fascinated — fascinated by a 60-year coaching career, fascinated by the Grand Experiment, fascinated by his motivations and values and the apparent and interesting contradictions of his personality. There have been other books written about Paterno, good books. It seems to me that there is more to say.

I don’t know if this will make much sense, but the advantage of writing a biogr...