I like mountain biking by myself. I like being able to go where and when I want. If I feel good I can extend the ride. If I don't, I can cut it short. I have become quite self-sufficient riding alone.

But I also like riding with others. I've learned new trails and picked up a few techniques when in groups. Sometimes I'm one of the faster people in the group, sometimes I'm the one that the group is waiting for. I ride with others about 50% of the time.

If you're training to race, riding with others could be especially good if they are a little stronger than you. They'll pull you along. You will ride harder (trying to keep up). Riding with weaker riders won't be much help for your training if you're serious about racing. But those rides can be for fun & socializing. Also realize that you're helping them by pulling them along.

But if your group(s) don't ride often enough or hard enough, then it's back to self-motivation. And that has to come from within. Solo, I often ride the same loop and try to beat my best time. Other times I try new lines on certain sections. But I ride alone mostly because I really like riding.

What is it about road riding that you enjoy alone? Can you apply any of that to mountain biking? Or if you really don't like mountain biking alone, just road ride alone. That's great training for XC racing.