It is probably peculiar to aged people especially to dwell upon the development of theories for living. If one has any inclination at all to tell other people how to run their lives (as older people so often do), it is expedient to have in one's arsenal a collection of theories to apply to the situation at hand. Not that these theories are only for others; indeed, the compelling feature of any really good theory is that one knows only too well how clever it is from having used it skilfully in the conduct of one's own affairs.
Obviously the cultivation of theories is prompted largely by the nature of one's activities; and the scope of theories is proportionally large as the activities are varied. For example, we could have a theory about fishing or pheasant hunting, the sort of thing that would appeal to the sportsman. No doubt there are theories about tennis, and golf of course (that one's pretty hackneyed I would imagine). Those of us who are in business tend to dwell more upon commercial theory, but again I'm quick to add that the realm of theory is usually reserved for those who are over the hill, or at least getting there rapidly. Youth, as in most matters, is more inclined to roll with the punches, on the assumption that no amount of thought could ever have anything useful to do with the prediction of an outcome. And yet, as one sadly discovers only later in life, nothing could be further from the truth.
A theory is part of that fuzzy area called abstract thinking. It's like a witty saying, something of general application, a concept without thinking of a specific example. The danger, however, is that its resourcefulness may exist only in the mind, not in reality. It is on this point that many theories become snagged and tend to lose their momentum. For a theory to maintain its thrust, it must somehow be grounded, otherwise it is merely the recitation of unattached intelligence, a rhetorical device which does little other than confound and irritate the audience (particularly useful for the likes of politicians, for example, when speaking in the House or to the media, or to an annoying constituent).
While I haven't said as much, it is also true that a rewarding theory may be usefully shared with those to whom one feels inclined to be a mentor. It is the happy accident of getting old to discover some secrets worth sharing with younger and inexperienced people. Such knowledge, as with any subtle thinking, is always only truly imparted if it can be done in simple terms. The moment the theory becomes complicated, the thread is lost! Theories must in effect speak for themselves, almost as self-evident truths.
As one learns to live by these hard-earned theories, the world is essentially turned upside down. Where once the motivation came from such and such a resource, now it comes from the complete opposite end. This result is not surprising, when one recalls that the abstraction of theories is to move from the particular to the general; whereas, life in the trenches is more often than not moving from the general to the particular. To continue the metaphor, a good deal of the appeal of theoretical thinking is that it uplifts one from the muck of daily living, removing one from the fray, allowing one to be resourceful and productive without getting your hands dirty. Of course you still need a theory that works, but that's what living and getting old is all about.