There’s some analogy to be had between a ghostwriter and a tailor—both have got to make their client look well cut and elegant, and maybe conceal the flaws or the flab.

I once had some suits made by a retired Savile Row tailor called Harry Cooper for a good price. He was a gifted cutter of cloth, but on one final fitting something didn’t seem to sit well. “It’s nothing to do with the suit,” said Harry, curtly. “It’s the inner man.” No answer to that. What can you do about the inner man? Well, there are tricks, which Harry knew, and he fixed me. A tailor, maybe a butler, too.

A friend was ghostwriting for a famous musician, while I was doing the same, in my case for Keith Richards. “How do you get on with your gentleman?” my friend asked. “My gentleman is being very difficult,” he said. “He won’t let me talk to any of his friends.”

That would have gone against my first trick for ghostwriting: unless a subject is already an accomplished, self-examining writer, novelist, or diarist, no one can successfully, or entertainingly, review their lives by themselves. They will leave half of the good bits out. Somewhere in Life, by Keith Richards, he asserts that “memory is fiction”—a version of the royal riposte “Recollections may vary.” Sam Shepard, the actor and playwright, waved his copy of Life at an audience, recommending, admiringly, this nugget of truth from the pen of Keef.

Friends will trigger memories lost in the lacunae of time, which the writer can retell. Friends keep the story honest; they add wit and the all-important tone of self-effacing humility in the stories the writer can allow to be retold. My friend was writing with one arm tied behind his back, and it showed, to his chagrin, in the final product.

My first trick for ghostwriting: unless a subject is already an accomplished, self-examining writer, novelist, or diarist, no one can review their lives by themselves. They will leave half of the good bits out.

Spare, Prince Harry’s memoir, didn’t have any of this, evidently. Beyond the fury and desire for atonement, no quest for the inner man was on the cards, as was the case in his ghostwriter J. R. Moehringer’s much-praised book with Andre Agassi.

Moehringer didn’t have at his disposal tales of achievement, fascinating friends, mentors, discoveries, creative breakthroughs. He is reported to have done a good job with what he had—a mass of new details on stories already known, some tabloid fodder we didn’t know (cocaine, the roll in the hay), and the descending arc into denunciation and piety. His main task was to write with pace.

Nor was it his task to improve Harry’s prose, in case it spoiled the authenticity. Philip Hensher wondered whether it was Harry’s or Moehringer’s description of the elephants at the Okavango swamp and who was responsible for the phrase “Her tears glistened in the spring sunshine.” He wasn’t enthralled either way.

Without wit, such a book will be charmless and unsympathetic.

J. R. Moehringer is reported to have done a good job with what he had—a mass of new details on stories already known, some tabloid fodder we didn’t, and the descending arc into denunciation and piety.

In the two published autobiographies I have worked on, some of the funniest and most revealing moments came from the outside.

For surrealism there was the story the producer Don Smith told me about Richards’s forceful mother, Doris, coming to New York when Richards was rehearsing with his band the X-Pensive Winos, a moment when Jack Daniel’s and other stuff was flowing hard and beginning to impair their performance.

It was an incident Richards had forgotten. Doris was watching through the studio glass. The band had been talking for 20 minutes. Smith had shown Doris the talkback button, and she hit it and screamed at Richards, the great Waddy Wachtel, and the great Steve Jordan, “You boys stop messing around there and get to work. This studio is costing money. Nobody understands what you’re saying anyway. I’ve flown all the way from bloody England. I don’t have all night to sit around listening to you yapping about nothing, so get to bloody work.”

“So thanks to Doris’s sudden burst of wrath,” wrote Richards, “we renewed our labours.”

In the two published autobiographies I have worked on, some of the funniest and most revealing moments came from the outside.

Then there is the story of David Bailey, whose memoir, Look Again, I ghostwrote. When I sensed that Bailey wasn’t being entirely honest, or perhaps was over-romanticizing his relationships with some of the women in his life, I put them together and recorded the dialogue, then printed some of it in the book. First Jean Shrimpton, and then Penelope Tree, his model and girlfriend in the 1960s. At lunch with the three of us, there was a major disagreement about the when and where of the first kiss, as in:

Bailey: That was the first time we did it.

Tree: I swear to God it was not.

And then their breakup:

Tree: I packed two suitcases containing clothes and books and left.

Bailey: I couldn’t find you. You went to Barbados. Then you went off somewhere in the Far East.

Tree: No, first I went to live in a valet’s room on the top story of the Ritz. Which sounds fun, but it wasn’t.

Bailey: I tried to get you back.

Tree: How come I didn’t know about it then?

Keith is right. Memory is fiction.

Or was it me who said it? I can’t remember.

James Fox is a London-based journalist, author, and a co-author of Keith Richards’s memoir, Life, and David Bailey’s memoir, Look Again