I have discovered that even in some sports and other professions where work has to be mostly done alone, it is better to work side by side with somebody.
The problem is one of motivation. I've realised that you are most motivated when your energy levels are high and least motivated when your energy levels are low. So really motivation rarely helps when you need it the most :) It is only the most highly motivated can actually work consistently, even when they're low.
As for us mortals, it's better to work with someone. When your motivation is low, the other person can prod you into working even when you don't want to. And you can prod him or her into working when he's down. It sort of balances the spirit....