A group of characters are on a quest, and on the way they pick up other characters who want to get to the same place.
You're on a quest. Maybe it's to defeat an evil wizard, maybe it's just to find a new home, but it's sure to be a long journey and you have to do it on your own. However, who's that on the side of the road? It turns out he wants to reach the same place as you. Even though his reason for doing so may be different from yours, he decides to come along. As you progress further you find yet another character, and he'd also like to come with your group. And then you meet yet another, perhaps more... By the time you reach your destination your group may now have five members, and even though everyone has to fulfill their individual goals you can do it as a team rather than separate.