I had never heard this quote/saying, so I looked it up.
Turns out, it came from Tom Selleck. Reddit says, "It’s from a line he spoke in the TV series “Blue Bloods “ as character Frank Reagan."
Most of us had only ever heard the term, "Life isn't fair," which of course, is obvious, that is axiomatic.
And, yes, of course, death is fair, as it comes to us all.
Of course, no one is under any "obligation," per se, to be a decent human being, the tenets of most religions, and indeed, evolutionary biologists believe that helping each other, and cooperation, is part of our DNA. In fact, they believe it is part of all mammalian DNA, it is part of a mammal's evolutionary strategy. You can see all mammals, have an innate, almost compulsion, to love, and to help each other.
You see this, throughout the animal kingdom.
So? Basically, what I am trying to say, don't be good to others for their sake, do it for your own. It is in your DNA, it is good for your soul and your mental health, it will bring you peace and happiness. And that? You can take to the bank. It is even based on science!