Tomorrow is a question mark. You can't know what tomorrow will bring. It could be the greatest day of your life; it could be the last day of your life, which is sometimes the same thing.
"You have to count on living every single day in a way you believe will make you feel good about your life -- so that if it were over tomorrow, you'd be content with yourself."
How do you become "content with yourself"? A contented person is probably optimistic and confident. He probably has found his purpose in life. He has his support system in place. He doesn't worry what tomorrow will bring.
What if tomorrow were the end? Would you have accomplished everything you needed to in this life? Would you say to yourself, "Self, you did well."?
If I were gone tomorrow, what would you say to me today?