The most important idea I got from it is something like: You gotta practice to get good at things. People that are better than you at things very likely practiced _more_ and/or _better_ than you. Other factors matter very little in comparison.
The book goes deeper into what "more" and the "better" mean here.
You may think this takeaway is obvious, but the extent of it certainly wasn't for me, and I can tell it isn't for a lot of the people I talk to.