"Wisdom rests in the heart of the one who has understanding, but in the hearts of fools it is made known"
This is a very interesting proverb. It says that wisdom, which is the ability to discern the triple-win choice or the triple-win action, is at rest in the soul of the person who has this penetrating quality of understanding. Understanding is that ability to see the connections between things and between people and between choices and actions. The person of understanding can penetrate beneath the surface independence of things, people, AND choices and can analyze how they fit together; how one thing caused another or will cause.
When you can understand how the reactions of the various variables will be, then you can make the wise decision. It is almost like being able to look into the future.
You can predict with a high degree of probability what will happen if you say this or do that or if you don't do this or you don't do that. This means that if you are inclined to choose wisely, then you will know which choice is the wise one.
On the other side of the coin, it is easy to see that what the fool is doing is not the wise course. When the selfishness of a person takes over this person can have all kinds of messy problems that did not need to take place. Unfortunately in our culture we want to take away from people the instant feedback that selfishness brings. We want to protect them so that they do not realize that they have made a foolish choice.
Solomon is saying...if you watch long enough you will see people tell you what not to do. Have you seen any of this lately?