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.
The line is what's fair, appropriate, or required, as distinct from what's generous, in light of the defined quid pro quo relationship between parties. As mentioned earlier, you should expect people to behave in a manner consistent with how people in high-quality, long-term relationships behave--with a high level of mutual consideration for each other's interests and a clear understanding of who is responsible for what. Each should operate on the far side of fair, by which I mean giving more consideration to others than you demand for yourself. This is different from how people in most commercial relationships generally behave, as they tend to focus more on their own interests than on the interests of others or of the community as a whole. If each party says "You deserve more," "No, you deserve more," rather than "I deserve more," you are more likely to have generous, good relationships.