The Vilna Gaon lived with this sense of the fleeting opportunities this world presents us.  Shortly before he died, he was seen holding his tzitzis and crying.  He explained to his followers, “Soon I will be leaving this world.  Here, for just a few pennies, I can buy tzitzis and fulfill the mitzvah every minute of the day, and day after day.  Before long, I will be in a world where I will not be able to purchase that opportunity even for millions.” ~ The Pirkei Avos Treasury