"Self-assessment leads to action, and lacks meaning without it." -Peter Drucker
Mr. Drucker, the father of modern management, nails the essence of improving as a musician with this quote. And he was not in any way discussing music.
Without self-assessment there can be no real improvement on any task. But equally important, once you gain the knowledge that self-assessment offers, if you don't take action, you might as well have skipped the assessment in the first place.
Are there any weaknesses in your playing that you've acknowledged yet failed to take action to resolve? If so, what are you waiting for?