Example: You drive your car faster than the speed limit. You're probably doing it because you feel like you have a reasonable need (you're late for something, etc), not because you just inherently like to be a jerk and drive too fast everywhere.
On the other hand, if you see someone else speeding, you're more likely to think they're doing it because they're just an unsafe asshole, and less likely to think they're doing it for a legitimate reason.
https://en.wikipedia.org/wiki/Actor%E2%80%93observer_asymmet...