How do you understand the sentence?

Well, the thread is jilted...

I take it to mean you should stretch yourself beyond your comfort zone to experience "real" life. Staying within one's comfort zone is certainly one way to live your life, but the author believes there's more to life than what we sometimes call "the daily grind" of eat/work/sleep. He's extolling us to try new things and to take chances/risks in order to fully experience what life has to offer.

It means that if you stay within your "comfort zone" in life, then you will never experience the unknown, take risks or grow beyond what you have always been. It encourages you to stretch beyond your boring life and begin to live an exciting life.