JK Rowling revealed the "triumph" of getting her first Harry Potter novel published in America was soured by the fear that her next work could never match its success.
The author said she was always confident readers would like her books, provided she could persuade a publisher to take them up in the first place.
In a conversation with DJ Lauren Laverne for the Guardian's Weekend magazine Rowling, 50, also told of how she sought advice from media mogul Oprah Winfrey on how to cope with being rich and the joy of being rejected while writing under a pseudonym.
Rowling said: "I did have a belief, with Harry, that the difficult thing would be persuading someone to take it, because it didn't fit. People said children's books had to be half the length, and what an old-fashioned subject, a boarding school.
"I did have this feeling that the difficult thing would be persuading someone to publish it - but that if it was, people would like it."
Rowling revealed how she was filled with doubt immediately after landing a US publishing deal in 1998 for the first Harry Potter book, saying: "From the outside, I'm sure everything looked amazing.
"But in my flat, where I was still a single mum and I didn't know who to call to do my hair, everything felt phenomenally overwhelming. For the first time in my life I could buy a house, which meant security for my daughter and me, but I now felt, 'The next book can't possibly live up to this.'
"So I managed to turn this amazing triumph into tragedy in the space of about five days."
The instant wealth that came from her Potter novels was "very frightening", and Rowling said she was grateful for the opportunity to quiz Winfrey on how to deal with great fortune after starting out in life poor.
She said: "She was someone who didn't grow up rich, then suddenly had money and no one to talk to - and you don't meet many women in that position.
"She said to me, 'Have you accepted that you will always be rich?', and I definitely haven't. And I said to her, 'Have you?', and she said, 'Yes, I know now that I will be rich for ever.' That hasn't kicked in."
Rowling also said that receiving rejection letters from publishers for manuscripts she had written under her pseudonym, Robert Galbraith, was liberating and left her feeling "thrilled", as she was being judged for her writing and not purely on her fame.
She also revealed she would have had more children if she had been younger when she first became a mother, at 39.
:: The full story is in today's Guardian weekend magazine.