Principles are ways of successfully dealing with reality to get what you want out of life.
Ray Dalio, one of the world’s most successful investors and entrepreneurs, cites principles as his key to success.
Earlier, I mentioned that the unique abilities of thinking logically, abstractly, and from a higher level are carried out in structures located in the neocortex. These parts of the brain are more developed in humans and allow us to reflect on ourselves and direct our own evolution. Because we are capable of conscious, memory-based learning, we can evolve further and faster than any other species, changing not just across generations but within our own lifetimes.
This constant drive toward learning and improvement makes getting better innately enjoyable and getting better fast exhilarating. Though most people think that they are striving to get the things (toys, bigger houses, money, status, etc.) that will make them happy, for most people those things don't supply anywhere near the longterm satisfaction that getting better at something does. Once we get the things we are striving for, we rarely remain satisfied with them. The things are just the bait. Chasing after them forces us to evolve, and it is the evolution and not the rewards themselves that matters to us and to those around us. This means that for most people success is struggling and evolving as effectively as possible, i.e., learning rapidly about oneself and one's environment, and then changing to improve.
It is natural that it should be this way because of the law of diminishing returns. Consider what acquiring money is like. People who earn so much that they derive little or no marginal gains from it will experience negative consequences, as with any other form of excess, like gluttony. If they are intellectually healthy, they will begin seeking something new or seeking new depths in something old--and they will get stronger in the process. As Freud put it, "Love and work are the cornerstones of our humanness."
The work doesn't necessarily have to be a job, though I believe it's generally better if it is a job. It can be any kind of long-term challenge that leads to personal improvement. As you might have guessed, I believe that the need to have meaningful work is connected to man's innate desire to improve. And relationships are the natural connections to others that make us relevant to each other and to society more broadly.