"The development of genuine expertise requires struggle, sacrifice, and honest, often painful self-assessment. There are no shortcuts."<p>Makes sense; a 'solid grasp' is like a solid algorithm: it's not solid until it can handle anything you can throw at it.<p>But the amount of time 'expertise' requires can vary a lot. Mozart had the technical expertise in music to write a fairly decent fifth symphony when he was nine. Beethoven's first symphony (technically superior, <i>emotionally</i> much superior) came when he was forty.<p>So it seems a good idea to distinguish -technical- expertise from -mature- expertise (much more familiar with all the special cases and anomalies). (Marriage takes longer to decide on the third time.)