Why did Anne call herself the best and the sharpest critic of her own work?

Anne cites herself as her harshest critic because she believes hereself to know what is good and what isn't.

"Eva's Dream" is my best fairy tale, and the odd thing is that I don't have the faintest idea where it came from. Parts of "Cady's Life" are also good, but as a whole it's nothing special. I'm my best and harshest critic. I know what's good and what isn't.