The Internet projects that there have been 110 billion human beings collectively who have lived on this planet since Lucy, 7 billion now. This calculates to 14 dead people per 1 alive now.
It is my personal conviction that the average human lifespan potential is 100 years. Since our genes have not changed in the intervening millennia it means that all of the 110 billion had a 100 year life expectancy potential.
Therefore if we multiply 100 years times 110 billion humans we can calculate the sum of 11 trillion potential years of life.
But if we died collectively around age 30 of multiple threats (principally starvation) it means that we have failed to exploit the human potential of maybe 8 trillion years of life power. The specific scientific definition of power is rate of doing work. So if we humans could have worked for these 8 trillion additional years ponder a moment how our world would look, today. This shortfall of human potential reality is massive and sobering.
My personal answer to the basic question "Why live? is "To do the most good of which I am capable," which correlates exactly to the amount of life power that I can bring to the task. I recall William James's admonition, "We live lives inferior to ourselves." To gratify our response thereby mandates that we seek and achieve our potential of 100 healthy, powerful years, and reject the shortfall that characterizes nearly all of our 110 billion ancestors.
If this proposition seems egg-headed to you then I stand convicted of having an oval cranium.