At lunch, I received a fortune cookie that said
LIVE EACH DAY AS THOUGH IT IS YOUR LAST
and when I thought about how I would live my last day, this seemed like absolutely terrible advice. If I knew I was dying tonight at bedtime, assuming I didn't spend the day moping or railing against the cruelty of my fate, I would surely live the day in a more or less hedonistic fashion. Between phone calls to tell people I loved them (which would surely get old if I did it every day), I would eat rich foods (no vegetables unless perhaps a creamed spinach came my way), blow off work and school, and just generally try to relax and have a good time.
So, how ought one to live each day? The sort of obvious answer is that you should live it in accordance with whatever you know about it. If it's your last day to file graduate school applications, you ought to file them. If it's your first day of law school, you should probably go to class. But the idea behind "live each day as though it is your last" is surely to cast some kind of extra perspective to help you do better than you might otherwise. So in that vein, what would the good advice be?
I think you ought to live each day as though you're going to live a long time. What will you see when you look back at this time in your life, and what do you want to see? Will you see yourself working hard to get what you want? Will you see yourself laboring futilely because you never thought about your actual priorities? Will the whole decade disappear in a blur of tv-watching and beer-drinking? Will this be the time you saw the first glimmers of the theorem that eventually won you the Fields Metal?
I remember something C.S. Lewis wrote. He said that since we are going to live eternally (a believe I don't share, obviously), we ought to mind our personality traits and trends. If you find yourself growing more irritable over time, then carried out to eternity, this would become hellish. So we ought to spend our time, at the very least, trying to improve our characters across the board. That's not a bad idea.
It depends on what you care about. Do you care how you are remembered? How do your actions today contribute to what you hope your obituary says? Or do you mostly care about having a good time, in which case, what are you doing today to either have a good time, or let you have a good time in the future? If you want to contribute to a field, are you working on your 10,000 hours?
One thing I care a lot about myself is memories. I try to choose activities that I remember later, that give my life some richness. Things that are relaxing and almost boring, like watching television, napping, or mindlessly surfing the Internet, do not have this property. Even if they are desirable in the moment, over time they blur together and add little to my life.
I find that difficulty is a good proxy for meaningfulness, for me. Learning new math, taking a long hike, reading a non-pulp (for once) book...these are things that stay with me. I look back at them and feel that something has really happened and I wasn't just taking up space or killing time. Even among similar activities, difficulty makes a difference. Eating a spicy rather than a bland food. Hiking uphill rather than flat. Strength training with low reps and heavy weights rather than light weights and high reps. Learning theoretical rather than practical math.
So for me, taking a more difficult path is somewhat key to feeling satisfied in life. Other people naturally work hard all the time, and may need to remember to relax and have a little fun. What works for you?