It goes like this: if your job/education deals with fashion, communications or medicine, you should feed your brain with information outside of those realms. Basically, if you're learning about rackets in your day job, don't spend your free time only thinking about rackets. You must read, absorb, listen, and learn about things that are different from you and your current knowledge. Watch foreign films, listen to podcasts about topics that confuse you, or intimidate you. Go outside of your information comfort zone. It's the only way that you will be able to contribute to your industry (and the world) in a meaningful way. Actively work harder at your curiosity.
You see, if you're learning about rackets all week, spend the weekend with the guy who makes the balls.