I mountain bike and scuba mostly solo and white water kayak solo about a third of the time. This is through a combination of circumstance and choice. In all three, solo violates conventional wisdom on safety. I don't see this as reckless though, if you have the competence to understand the risk and pick your spots. This means a scenerio well within your capabilities and one where multiple things have to go wrong to create a threatening situation. Besides the social benefits, group outings to provide a support structure that lets one go a lot closer to the edge. Accordingly I would probably be better on a bike today if I didn't solo so much. As others have mentioned though, it has lots of benefits and I don't look back on the choices.