I read a couple of great books this year about human behavior, and this was one of the most interesting and profound. Both Jenn and John Doerr urged me to read it, and I’m glad I did. Everyone knows that a good night’s sleep is important—but what exactly counts as a good night’s sleep? And how do you make one happen? Walker has persuaded me to change my bedtime habits to up my chances. If your New Year’s resolution is to be healthier in 2020, his advice is a good place to start.