And besides, being smaller has its perks—I’m much better at hiding in small spaces when it’s her turn to do the dishes.

At her high school basketball championship, the older sibling stands in the crowd. As she dunks over a defender, he screams louder than anyone. Later, she picks him up in a bear hug that cracks his back. “You did good, kid,” he whispers. “I learned from the best,” she replies, setting him down gently. He straightens his shirt, looks at the ceiling, and smiles. Being the little big brother isn't so bad.

"Every time we meet someone new, they address her first as the 'big sister,'" says Sarah. "I’m 5’2” and she’s 5’10”. I’ve started carrying my ID just to prove I was born first. It’s a constant exercise in ego management, but it’s also a great icebreaker at parties." 5. The Built-In Training Partner