Eye for an eye (and a tooth for a tooth)
Adam Grant, in his book Give and Take, explains that success is not about winning a competition but making a contribution. In Grant's view, while "taking" seems like the shortest path to the top, "takers often fall by the sword of karma police." Grant's research "revealed that in the long run, giving is a more sutainable route to success… if you are thoughtful about how you do it."
The reason to help others, however, goes beyond being afraid of the "karma police", or because studies show that givers fare better. Seth Godin, discussing Zig Ziglar on Tim Ferriss's podcast, shares the idea of helping others as an act of generosity in itself and not because of the expectation of getting something back in the future, even indirectly:
He [Zig Ziglar] would say, “You can get everything in life you want if you help enough other people get what they want,” as a way of encouraging self-interested, short-term people to see that the best way to get ahead was to do a favor for someone else because that forced empathy opened the door to making a sale.
And what shifted for me over time was how about "you can get everything in life" you want and "you can help other people get what they want", but they’re not one gets you the other one. That what we have is the chance to hold open the door and let somebody else go in, not because we want them to give us something in return, but simply because holding open the door is, in itself, a significant useful act that will fuel our next cycle of work.
Helping others is significant in itself because the one who gives becomes a better person. Just as the first effect of stealing something is that you become a thief, by helping others without the expectation of future returns you become a more generous person. It changes how you see the world and opens the door for you to make your best contribution.
We should be far beyond modern incantations of the ancient law of "eye for an eye and a tooth for a tooth".