When my younger sister was in college, she needed help with the down payment for a new car. I wrote her a cheque — coincidentally, her birthday was just around the corner — and sent it in a card, with the understanding that when she was solvent, she’d pay me back. Almost a decade later, that portion of my coffer remains empty; in fact, it’s permanently closed, since the one time I suggested she might pay me back, it caused a battle so ugly that my father had to step in to break up a fight between his adult daughters.