So let's say if in your life span, you consume X amount and produces X amount, you have just.... lived by not burdening anyone else.
But let's say if you consumed X amount, but produced Y amount and Y-X is much greater than zero and you contributed to .. well, not on yourself, be it your offspring, your community, whatever... You just made your life much more meaningful.
This equation is only correct if the only things of value are those that are monetarily compensated. This is (IMO) not the case. I don't think that what I do (programming) contributes more to society than a teacher, yet I am compensated much more than most teachers. To say nothing of homemakers...
Now, if you are really good at making money, and not very skilled at other things like teaching or parenting, then your highest and best use to society may very well be working as long as possible and amassing a fortune. I don't think this applies to most people, but I agree it is worth considering.