Persistence isn’t just key — it is everything. Getting in the ring is hard, but staying in the ring is even harder, especially when you feel beaten down, tired and alone. Successful entrepreneurs will readily tell you about the good times, their secrets to success, and even their mistakes (with a ready helping of how they overcame them), but they will rarely mention the times they were ready to throw in the towel and do something else. The truth is that everyone has those moments, and the guys you read about on the cover of Fortune were the ones that didn’t quit at them.