To be prudent amounts to making sure that one takes good care of oneself in all important areas of one's life. Health, wealth, family, friendship, understanding, etc. are all in need of good care so that one will achieve and sustain one's development as a human individual. It all begins with following the edict: "Know thyself!"
All those folks who make an effort to keep fit and to eat properly are embarking on elements of a prudent life. Unfortunately, the virtue of prudence has been undermined by the idea that everyone automatically or instinctively pursues his or her self-interest.
We all know the rhetorical question, "Isn't everyone selfish?" Because of certain philosophical and related doctrines, the answer has been mainly that everyone is. In the discipline of economics, especially, scholars nearly uniformly hold the view that we all do whatever we do so as to please ourselves, to feel good. No room exists there for pure generosity or charity, for altruism, because in the final analysis everyone is driven to act to further his or her own wellbeing, or for carelessness, recklessness. If people do not achieve the goal of self-enhancement, it is primarily out of ignorance – they just don't know what is in their best interest but they all intend to achieve it and even when they appear to be acting generously, charitably, helpfully and so on, in the end they do so because it gives them satisfaction, fulfills their own desires and serves their idea of what is best for them.
This is not prudence but what some have dubbed animal spirit. People are simply driven or motivated to be this way, instinctively, if you will. The virtue of prudence would operate quite differently.
One who practices it would be expected to make a choice to pursue what is in one's best interest and one could fail also to do so. Practicing prudence is optional, not innately produced. Like other moral virtues, prudence requires choice. It is not automatic by any means. The reason it is thought to be so, however, has to do with the intellectual-philosophical belief that human conduct is exactly like the behavior of non-human beings, driven by the laws of motion!
Once this idea assumes prominence, there is no concern about people having to be prudent. They will always be, as a matter of their innate nature. What may indeed be needed is the opposite, social and peer pressure to be benevolent or kind, to adhere to the dictates of altruism, something that requires discipline and education and does not come naturally to people.
It would seem, however, that this idea that we are automatically selfish or self-interested or prudent doesn't square with experience. Consider just how much self-destructiveness there is in the human world, how many projects end up hurting the very people who embark upon them. Can all that be explained by ignorance and error?
Or could it be, rather, that many, many human beings do not set out to benefit themselves, to pursue their self-interest? Could it be that human beings need to learn that they ought to serve their own wellbeing and that their conduct is often haphazard, unfocused, even outright self-destructive (as, for example, in the case of hard drug consumers, gamblers, romantic dreamers, fantasizers and the lazy)?
It seems that this latter is a distinct possibility if not outright probability. It is a matter of choice whether one is or is not going to be prudent, in other words. And once again, ordinary observation confirms this.
One can witness numerous human beings across the ages and the globe choosing to work to benefit themselves, as when they watch their diets or work out or obtain an education, and many others who do not and, instead, neglect their own best interest. Or, alternatively, they often act mindlessly, thoughtlessly, recklessly, etc.
The contention that they are really trying to advance their self-interest, to benefit themselves, seems to be one that stems from generalizing a prior conviction that everything in nature moves so as to advance forward. This is the idea that came from the philosopher Thomas Hobbes, who learned it from Galileo who took it from classical physics.
Accordingly, acting prudently, in order to advance one's wellbeing, could be a virtue just as the ancient philosopher Aristotle believed it to be. And when one deals with financial matters, careful investing would qualify as prudence, just as is working out at a gym, watching one's diet, driving carefully, etc.