I ride solo 99% of the time. I love riding so the motivation is doing something I enjoy. I decide what my goal is for the day (speed, power, distance, recovery etc) and just start laying down the miles toward that goal. What really motivates me is the joy from being able to do something that most cannot. If/when the time comes that I can't ride then it will take some real motivation to get through the day. For now it's easy.