> If you consider the number of people that want to lose weight, quit smoking, or get better at something, I’m probably wrong about the market size. It’s huge.

Everyone wants to improve something (or everything!) about themselves. Most people have a sense of what that is, and what they should be doing. Stop smoking, go to the gym, get more sleep, eat better, spend less money, make more money, etc. A personal analytics system may help someone optimize their life from seeing the hidden details, but I claim that the steps to self-improvement for most people are fairly obvious. The problem in self-improvement is not lack of data, it's how to execute on the obvious known fixes (how to stop smoking, etc).