The average life expectancy is approximately 78 years. When you are young that seems like a very long time, but as you get older it seems to go faster and faster. By the time you are half way there you start to take stalk of your life and evaluate your accomplishments. For many these accomplishments are in terms of educational and career success, house and car purchase, marriage and kids. But what if the the average life expectancy were 40 years? 30 or 20 years? How would this affect our priorities and the criteria for which we measure success? As the life expectancy decreases obviously accomplishments that would take relatively longer to achieve, like successful career achievements, would become less and less obtainable, until finally, in the extreme case, if life expectancy reached below reproductive age, the species would become extinct. Some insects, like the fruit fly, only have a life span of 2 weeks, so they just have enough time to eat, mate, and lay eggs before they die and the cycle is repeated.
Therefore, as life expectancy decreases we come to the most basic achievement--the propagation of the species. However, what if we were to move toward the opposite end of the spectrum? What would become more important as the life expectancy increased? Naturally, if we have more time available to us we could accomplish more things. But what would be the ultimate accomplishment if we were given a hypothetical life expectancy of 1000 years? 10,000 years? Infinite? If we could live so long that we have seen and done everything there is to be done, what would we consider to be the ultimate achievement? World peace? Given the nature of humanity, and as evidenced by thousands of years, this will never be achieved. But let us be optimistic and say that it is possible and we achieve it, then what? Suppose we discover the answer to "Why are we here?" If that could ever be answered and we have achieved it, then what else is there to work towards? If all is accomplished and we live the rest of eternity forever happy, would that not get boring?
This brings me to the point of this hypothetical consideration of life expectancy. Without something to look forward to each day, and without obstacles to overcome to obtain them, what is the point of life? Therefor, do not concern yourself over how many years you have to live or the strife you endure during the years you have. Rather, enjoy and be thankful for each day, for each day is an accomplishment in itself and the more strife that is overcome, the greater the accomplishment.