I've found lack of direction to be my biggest issue. I've got a job that, thankfully, gives me a decent work-life balance (if not a great pay to go along with it), but I just can't bring myself to do anything during my time off because I don't know what to do.

Though, that's not to say discipline isn't an issue as well. I've had several ideas, and never really followed through because of lack of discipline/not seeing how it's going to help me earn money, etc.