Every man is, no doubt, by nature, first and principally recommended to his own care; and as he is fitter to take care of himself than of any other person, it is fit and right that it should be so.
Note carefully three features of this insight from Smith. First, this description of the practical domain of each person’s attention and interest is completely consistent with Smith’s description of human motivation that most famously runs through much of The Wealth of Nations.
Second, Smith does not say here (or in The Wealth of Nations) that human beings are narrowly self-interested – or greedy; he does not say here (or in The Wealth of Nations) that people have no genuine concern for the well-being of others, even if those others are strangers; he does not say here (or in The Wealth of Nations) that people care only about accumulating maximum possible financial or material well-being.
Third, Smith nevertheless had no romantic delusions about the ability or interest of John to superintended the life of Jane in ways that will generally improve Jane’s well-being. However faulty Jane might be at running her own life (as judged by Jane’s own goals), she is, as a rule, much more likely than is John to run her life with some success. Ditto, of course, for John and his own life.