If you're doing something you love, it doesn't matter that it's challenging. You can keep going for a long time as long as you're motivated- just make sure you choose the right starting point. If you're lucky, as happened with Stephen, Your inclination may even become a vocation.
Chris Guillebeau, The Happiness of Pursuit: Finding the Quest That Will Bring Purpose to Your Life
challenge, chris-guillebeau, motivation, the-happiness-of-pursuit