I believe that we tend to overestimate the presence of skill in our own positive outcomes. And that we tend to overestimate the presence of luck in our negative outcomes.

When we view others, however, that gets flipped. We tend to overestimate the presence of luck in other's successes. And we overestimate the presence of skill (or lack thereof) in their negative outcomes.

In short: we lose because we're unlucky. They lose because they suck.

They win because they're lucky. We win because we're amazing.