I like this quote by Thomas Mann, a German-born novelist, short story writer, essayist and Nobel Prize in Literature winner in 1929. His writing journey and amount of work he produced certainly gave him the insight shown here.
Why is writing more difficult for the 'writer' than for others? I think it comes down to a true writer is striving for perfection. They are the ones hoping, dreaming, and praying they can sell what they write and are well aware only the best work is chosen for publication.
The true writer also wants to offer readers something that will inform and entertain. The true writer puts words together with an intensity that the nonwriter cannot truly understand. He/she also understands how difficult it is.
The real writer cares about his/her writing. It's not a matter of throwing something together to submit to an editor. Pride comes into play. Think about it. What a writer produces and offers an editor is going to be opened wide to the public if it is accepted for publication. I wonder how many writers had mothers who said Do your best. Those early admonitions become habits, and that's generally a good thing.
A real writer is concerned with reviews if they have a book published. It's much harder to write a book that receives four and five-star reviews than it is to hurriedly put something together and then maybe self-publish. Yesterday, I read a review in our Sunday paper of a nonfiction book that the reviewer thought had an excellent topic. He went on to say that it was a shame that it was so poorly written. Turns out the 'writer' of the book really was not a writer but someone interested and knowledgeable about the topic. The reviewer suggested he would have done better to use a ghostwriter. The ghostwriter would have most likely had to work a great deal harder than the guy who knew the facts but not how to put them together in a credible form.
If you are a writer who finds writing more difficult than the average person, go right ahead and pat yourself on the back. It is harder when you're striving for perfection. But, in the end, it's worth all that it took to write something you're proud of.

