I don't know when I will die.
The only information I have about my time on this earth is 1) that which I've already lived, and 2) that right now I am alive. It is reasonable to assume I will continue to be alive, because living like I'm alive -- instead of living like I'm dying -- is actually the most rational way to behave.
I understand the allure behind the "live like you are dying" sentiment. It's quaint because it's pithy. It inspires you to do awesome, crazy, brilliant things because truly, time on earth is short. You get, maybe if you're lucky or really healthy, 100 years. In the grand (in the truest sense of the word) scheme of things, 100 years is very brief. Factor in how you might not even get that many, and then consider how many of those years are actually available for active and independent life. Then, you might start to see your life as a window, between ages 18 and 60, to do awesome things. Again, if you get that much time. I agree with all of this, but I submit to the discussion one more notion, that the most attractive part of the "live like you are dying" quip is this: It reminds you that how you choose to spend your time is a gamble.
Under the "live like you are dying" paradigm, the gamble weighs time spent alive doing awesome stuff versus the time of your death. You could work really hard for 50 years and save a lot of money for your retirement, and then have an inspired and comfortable old age. But, then again, you might die before you retire, and then you'll have wasted all that time working for nothing! Live like you're dying, because if you don't, one day you'll be dead, with nothing but regrets under your belt. Carpe diem, go backpack Europe, because one day soon, you're going to die. And dead people can't backpack Europe.
I reject this, not because I reject the notion that one day I will die, but because of it.
It makes much more sense for me to live like I am alive right now, and alive for the reasonable and foreseeable future (if that even exists, because no one can actually foresee the future). Under this paradigm, I'm reminded of a similar gamble: time spent now versus how I want to spend time in the future. You see, if I choose to live like I'm dying, I have little to no incentive to invest in the future of the world, and the future for generations to come. I also have no incentive to invest in the future of myself, because the only future I entertain is one in which I am dead, and somehow that's supposed to catalyze me to feel alive now.
You know what would really catalyze me to feel alive right now? Knowing that I'm going to be alive a little longer and don't want to live a life I hate.
If I die tomorrow, I won't care that I didn't go backpack Europe or skydive or win a Pulitzer, because I will be dead. In addition to not being able to do awesome things, dead people also can't be sad about their old life. It's just part of being dead; losing sentience seems to just come with the package.
However, if I live like I'm alive, and I anticipate many years ahead, I am much more likely to spend my time now cultivating a good life. If things go as planned, and I live to an old age, maybe even to 100, I will want to look back on my life and consider all the things I did. I won't want to reminisce on the time I worked hard at something I hated for no return, not because I'll consider that a waste of time alive, but because it won't be interesting or have contributed to what it means to have a good life. I'll want to look back and know that I chose the best things I could, that I helped people when I could, that I loved people, that I made time to appreciate everything beautiful.
I don't want to live in fear of death, because that's no reason to make a good life today. I don't want or need to carpe diem if tomorrow, none of it will matter, because I'm dead. I want to live in hope of life, so that everything I do can be deliberate and thoughtful. I want to contribute to my health, to the environment, to the health of people around me. I want to believe in life because it's the only way to make a good one. I have to believe in life because otherwise, I don't need to seize the day, I need to get my last will and testament in order.
Death doesn't get to dictate how I live. Existence is demanding enough.