Balance. I end up working fourteen hour days when I feel motivated, burn out on those in about 2 weeks and then have a hard time getting myself back to getting anything done for another week. Over long-term, I would probably get a lot more done and be happier if I limited myself to being productive 6 hours a day every day rather than the other way, but getting the self-discipline to stop working and walk outside when you are on a roll is probably the most challenging thing.<p>I am not yet at a point where I can collect money from users; I suspect that once I get to that point, the hardest problem will be "how do I get more people to pay?" This seems to be completely different - it seems that right now I am my own enemy, whereas later it will be actual external forces.