Here’s Peter Roebuck talking about the three stages of a cricketer’s development—but I believe it also applies to writers:
It begins with natural ability that takes a fellow as far as it can. Then comes a period of introspection in which the complications of the game are encountered and, to a greater or lesser degree, resolved. Finally the player reaches the final stage of a hazardous journey, beyond complexity, towards full understanding. This third stage is called simplicity, but it is profundity.
The thing is, with a cricketer, it is easy to tell which stage he is at, with little scope of self-delusion. Phil Hughes and Mitchell Johnson know, from their results on the cricket field, that they need to work out a few things. But writing is a subjective matter, and many writers may not know when there are problems with their game. As a result, they’ll never then do the necessary introspection and hard work needed to take them to the next level. That is why, the most important quality for a writer is surely humility—writers must be brutal critics of their own work, and must ruthlessly employ what Ernest Hemingway called “a built-in bullshit detector.”
On the flip side, that often erodes self-belief. It’s a thin line.