The life of an entrepreneur can take founders to elevated peaks of accomplishment, and deep valleys of desperation. And the time to go from one to the other can be surprisingly short. Jason Lemkin has seen both several times. He’s learned that what matters more than skill or personal network is the individual determination to keep going. Looking back, most entrepreneurial journeys look more like a roller coaster than a well marked trail, and it’s only over when you decide it’s over.