Every day you’re alive could end up being one they study forever in history, so make sure to pay attention to it.” Her father’s words, once her mantra, now echoed in her mind like a taunt.

At this point Jenna was fed up with it. “It’s just one day,” she thought, “It doesn’t matter, I have plenty of time, I can deal with things tomorrow.” She could study tomorrow, she said, she’d work on new skills tomorrow.

Now, a reigning cliff diving champion and a Harvard student, she was the epitome of...