Dear Bryan, You’re probably at the piano, writing songs about things you know nothing about, like love and loss. Or doing vocal warm-ups so you can audition for that blasted show choir. (Don’t bother. You won’t make it until your senior year, and when you do, you’ll become a bigger nerd than you already are.) I do hope you’ll find time for this letter. I’m writing from the future, of course, to warn you about...