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If I was writing my first book and there was a well-known fiction author[1] with the same name as me, I might consider changing my pen name.
If I was writing a sports book and there was a existing sports author[2] with the same name as me I would urgently consider changing my pen name.
If I was was writing a book about cricket and I had the same name as a famous cricketer[3], I might consider the game was up and I had better start thinking of pseudonyms right away.
Because what chance is there of finding the new Peter May on Google?
[1] Peter May
[2] Peter May
[3] PBH May