1. That popularity won't follow you for nearly as long as a good - or terrible - GPA.
2. That no one is looking at or or thinking about you as closely as you are looking at or thinking about yourself.
3. That down the road you'll be glad you have a grasp of basic math - so you won't feel like a complete dolt figuring a waiter's tip, what percentage of your paycheck you can part with or how to convert dollars to Deutsche marks.
4. That you'll never have a job just to cover gas money, concert tickets and clothes again.
5. That the less-popular kids might make better friends than the cool crowd. Popularity stops mattering the instant you graduate. (At least it should.)
6. That you won't miss out on anything if you skip a few parties or cut short a couple of phone calls in favor of studying. You can have good friends, a good time and good grades.
7. That when those people say "These are the best years of your life," they mean it, though not for reasons you might think. They're the best years because - regardless of how worldly and jaded you think you are - you're still open to life. Never again will someone's saying "hello" to you in a hallway make your spirit soar for a week.
8. That the nerdy guys of the senior class will be the most sought-after men at your high school reunions.
9. That 40 is much closer than you think, and you will pay dearly if you forgo sunscreen.
10. That someday you will be sitting at your 70-hour-a-week job, thinking that those teachers you mocked actually have it pretty good: three months of vacation every summer and a job that actually matters.
11. That if you have the opportunity to learn something or do something, you should grab it.
12. That you'll be forgiven for many things. Yet one stupid decision can alter your life.
13. That by and large, the things you regret most in life are the things you didn't do.