[munificent]

Having a longer life gives you a greater total capacity to do and create meaningful things. But the meaning of any given fixed-time act is less if the lifespan is shorter.

Spending half your life writing a book makes that book more meaningful than spending a tenth of your life doing it. But you can only write two of the former versus ten of the latter.

Either way, this is a simple and dumb mathematical model, not a literal equation for calculating the actual value of a life's work.