If you think that the insecurity most newer writers feel goes away automatically when they are successful, there’s sad evidence that it ain’t necessarily so. In the recent exposure of a number of writers who wrote glowing Amazon reviews for their own books using a series of fake names, it came out that some of them also wrote reviews trashing the books of writers they considered competitors.
One of the guilty parties was mystery writer R. J. Ellory. He has since apologized for what he called a “lapse of judgment.”
Did he really need those extra reviews or to discredit his fellow authors? Not if sales figures and awards are anything to go by. Wikipedia says, “A Quiet Belief In Angels has sold in excess of 1,000,000 copies since its release, and has also been purchased for translation into a total of twenty-three languages. It was ranked third in the Sunday Times bestselling book list in the week of its review on TV. It was shortlisted for the Barry Award for best British crime fiction 2008,[6] the 7th Prix Du Polar Européen 2008 of the weekly French magazine Le Point, 'Le Nouvel Observateur′s Crime Writing Prize 2008, and the Quebec Booksellers' Prize 2008.[2]”
Of course it also says, “This article may be an autobiography, or has been extensively edited by the subject or an institution related to the subject. Please help edit it to conform to Wikipedia's neutral point of view, in line with the discussion on the talk page.”
Using one of his pseudonyms, "Nicodemus Jones" [Nicodemus Jones? Really? There’s certainly nothing suspicious about that name] Ellory described his book as a "modern masterpiece…All I will say is that there are paragraphs and chapters that just stopped me dead in my tracks . . . it really is a magnificent book".
To me it suggest that, at least for some writers, the insecurity remains even after they’ve sold a million copies.
I know it’s easier said than done, but try not to value yourself according to how your writing career is going, especially if you are never satisfied even when it goes well. It took me years to stop doing that and believe me, it feels so good when you stop!
(For friendly guidance from your initial idea all the way through to marketing the finished work, get a copy of my book, "Your Writing Coach." Nicodemus Jones called it, "The best book ever written in any language. I fainted from its sheer greatness." Wikipedia says, "It has sold more copies even than A Quiet Belief in Angels--Warning: this may not be true")