Many people wonder why they are not improving enough to become professional writers (in this case, he's talking about screenwriting, but it can be applied elsewhere).
And while you might not find this advice by John Truby incredibly encouraging, think about it this way. He says that everybody has flaws in their writing, even professionals. It's the inability to receive and use criticism that is the undoing of most amateur writers. Have an open mind and be receptive and maybe your fortunes will change! Now, this isn't the all encompassing advice for how to succeed at writing, but it is good advice.
The people that crash and burn are the ones that refuse to take criticism. Remember that, and you'll be ok!