Character Role Analysis
Faithful and Unfaithful, Good and Bad Friends and Siblings
Any time you have a super-sweet and pious girl she's got to have a wicked stepsister, and any time you have a courageous young guy he's probably got brothers or traveling companions who are gonna stab him in the back later. These tales aren't so big on detailed description, so they show rather than tell. That means that having contrasting characters as a recurring characterization tool can convey a lot of info relatively quickly.