Odds are that there are dozens of people way cooler than me who would benefit from the work that I can do in preparation for them.
Also, eternal life, like immortality in the annals of human history, is only something I can hope for. Making other people’s lives better is the only way I know for sure I can make a mark in the world.
As Bo Burnham puts it, “You pray so badly for heaven knowing any day could be the day that you die, but maybe life on Earth can be heaven. Doesn’t just the thought of it make it worth a try?”
I think Western society/individualism has erased a lot of this but for centuries before colonialism and still in a lot of indigenous and non-western societies, it's expected to respect your elders and take care of them. In turn, they should be aiming to build that respect for themselves and to be a good ancestor for those preceding them. You see this all across indigenous belief systems - your society/nature will take care of you just as you took care of it.
The reason nobody did shit for us is because those beliefs have been overridden by colonialism and individualistic mindsets. Humans aren't meant to be as selfish as we've become, that's why we're so unhappy.
Because someone else has already built it for us. It’s our duty to pass it on. And honestly it is the core of what it means to be human. Otherwise you’re a parasite who deserves what parasites deserve.
Not really how our monkey brains work generally. We're biologically programmed to do lots of things, like want to have babies (or at least sex and not be smart about it) and to take care of them. Not everyone does a good job, but historically speaking it's led to a population of a few hundred people turning into a few billion.
Because you are not the main character of the universe.
You will leave behind consequences for your actions. The consequences of the actions of others gave you the world you have lived in, as will the consequences of your shape the world of the future.
There is nothing after death and we all know that, so all there's left to plan for after you die is the legacy of what you did while you were here.
Speaking for me, I value the idea that the consequences of my life wind up being more positive than negative for future generations. I also value feeling like I've changed things for the better now, and so when I have a platform or any influence I aim for that.
If you don't care about any of that, please seek counseling. The rest of us will be better off with fewer narcissists.
I'm from yesterday. When I was a kid in the 70's, my tomorrow was the triumph of science, an evermore interconnected world of evermore educated people, the rule of individual rights and freedoms, the retreat of religion and magical thinking, fewer and fewer wars and the gradual end of poverty.
I'm very bitter today because somebody stole my future. But you can also argue that I, a man of yesterday, failed to shape the world of today too. We all failed, those of my generation.
If you're a person of today, you need to work towards a better tomorrow right now. Because if you don't, you'll end up regretting not doing it later in life like I do.
You build for tomorrow to leave something behind of yourself. The tree you planted, the painting you made, the building you built. They are parts of oneself that remain after our alloted time passes.
I like the idea that I was part of the foundation of something positive that will outlast a single human life time. All you have to do is not be a douch to positively impact. Maybe it's just a drop in a bucket but ocean is just a collection of drops of water.
From a purely cynical perspective: Species survival. Evolution has programmed us to desire offspring and try to ensure their ability to produce offspring. To do that, I need to make sure the world is livable for them and the next generations.
Small minded people see this and think "I just need to make it better for my kids not everyone". They're missing the big picture. They fail to see that we survive better if everyone is surviving better.
Not sure why this is so downvoted , it's an interesting question.
There are many things that made us shoot forward in the evolutionary arm race, but one the parts is the sharing of knowledge and values to our offspring.
Children want to learn from their parents, and parents want to teach their children in the same way they learnt from their parents.
The early humans who started this generational knowledge sharing fared better, and humans became more social and dependent on each other, while the humans focused on themselves more than their offspring perished.
It's in our nature to care for our next generation, in the same way the previous generation cared for us.
We are monkeys that with the benefit of lots of time have developed opposable thumbs, tools, and language. We used language to describe abstract concepts in words. One of those words is "legacy." Some people are driven to build one. Some are just altruistic. The urge to create offspring is also common and with it the hope your brats will fare well. There are your reasons why some people build for a tomorrow that never pays them back.
Consider also that somebody has built the road that leads to your house, the city you're in, the hospital you go to when you're sick. Civilization is a chain of paying stuff forward for those who come after you.