Earlier quoted context omitted.
Most people do not take care of their family because they think it's in their best interests. They often take care of their family for myriad reasons--e.g. a moral call to selflessness, sociocultural norms, a sense of familial duty, love, etc. The language of "best interests" really doesn't fit here. Taking care of an ailing parent is in no way connected to maximizing one's returns on anything (except maybe fulfillin…
You're missing his point. "Interests" is a technical term in economics which means something different from the common usage. In short, it means things you consciously seek for their own value. Love, being moral, fulfilling duties; all of these are interests in the sense economists use the term. NB: Economists largely study specifically monetary interest because it's something they can measure. A number of criticisms…
A principle assumption of many of the models underlying economic theories (including, but not limited to, rational choice theory) is that there is a unidimensional quantity, "utility", that aggregates a persons preferences and which individual decisions increase or decrease by definable amounts. Because money is widely fungible, and utility cannot be measured directly, money (e.g., the money people are willing to pay to get something they want, or the money they demand to do or give up something) is often used as a proxy for utility by economists, with the idea that all decisions have an (potentially zero) utility impact, and that utility impact can be stated in monetary terms.