Wayne Dyer
Dyer’s 1976 manual Your Erroneous Zones is one of the bestselling books of all time. It was also mostly cribbed from famed psychologist Albert Ellis’s practice of Rational Emotive Therapy, a fact Ellis pointed out to him a decade later. Ellis later said he was just happy his work was reaching so many people, though it might have been a different story if he’d actually needed the money.
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M. Scott Peck
It’s not necessarily notable that M. Scott Peck had lifelong habits of drinking, drugs, and infidelity — you can’t swing a dead cat in a bookstore without hitting an author in the same packed boat. But Peck’s bestseller, The Road Less Traveled: A New Psychology of Love, Traditional Values and Spiritual Growth, was uniquely preachy even among self-help books on these very topics. One publisher even rejected it as “too Christ-y,” although to be fair, that guy did love him some wine.