When I make an error and overshoot my target in any direction, it seems like a small error since both my target and the fallen frisbee are far away from me. When my partner makes an error, I am able to see precisely how far away from me the frisbee has landed.
We perceive two points far from ourselves as closer than two points near to ourselves, even if the two sets of points are both "in truth" the same distance apart.
I perceive my errors as more innocuous than they really are. I see my partner's errors, which affect me, with perfect clarity.
Can this be applied to other two agent scenarios where our actions affect others and their actions affect us? I would say so. The farther away we are from the consequences of our actions, the smaller we perceive them to be, and the more we overestimate our own abilities.
And by the way, the thought that I may be worse at frisbee than I already judge myself to be is a very scary thought. A very scary thought, indeed.