"Two years ago, we adapted a feature from Macworld into a book called 100 Things Every Mac User Should Know. The idea was to compile a bunch of tidbits—keyboard shortcuts, Finder techniques, and the like—that we thought every savvy Mac user should understand and feel confident about using: not ABC beginner stuff, and not truly esoteric expert-level maneuvers, but the kinds of things that mark you as experienced and informed.
Of course, there are a lot more than 100 such things. So we decided to revisit the idea, coming up with another 100 pieces of Mac-related information we think users should have at their command. So, yes: You now have 200 things you need to know.
As we said back in 2011: We’re sure you know a lot of the things we’ve listed here. But we bet that very, very few of you, if you’re really being honest, can say you know them all. Check them out, and let us know if we’re wrong."