The Freakonomics blog analyzes Han’s decision to come back and help the rebels in Star Wars.
Han understands that the Rebels have a dominant strategy of fighting. Knowing that, although he has no dominant strategy, and being the self-centered person he has already shown himself to be, Han realizes he is better off choosing to aid the Rebels and fight.
And Volokh Conspiracy follows it up with a serious point:
[Han’s] contribution is likely to be decisive to the outcome. After all, he’s got “the fastest ship in the galaxy,” and it can make mincemeat of Imperial tie-fighters. […] Now the serious part: Consider how different is the situation of most people suffering under oppressive governments from Han Solo’s. If any one of them tries to rebel, it is highly unlikely that their actions will have a decisive impact on the regime’s fate. On the other hand, they, unlike Han, don’t have the Millenium Falcon to escape in. If they defy the government, they will likely be caught and punished. Of course if all or most of them resist at once, they might well overthrow the state.