If you’re an entrepreneur, you’ve got to be mentally tough—or the world will break you. I learned that from studying the Spartans and from living it myself. The Spartan mindset is all about strength through purpose. Think about King Leonidas and his 300 warriors holding the line at Thermopylae. They didn’t surrender even when the Persian army surrounded them. They fought to the last breath because they had something bigger than themselves to fight for—their people. That’s what I want for you. Not just toughness for toughness’ sake, but strength that’s fueled by love, mission, and belief.