The metaphor perhaps means "A wise man's sense is in its place, ready to help and protect him; but a fool's sense is missing when it is wanted, and so is useless."

A wise man's heart is at his right hand - As the right hand is ordinarily the best exercised, strongest, and most ready, and the left the contrary, they show,
1. The command which the wise man has over his own mind, feelings, passions, etc., and the prudence with which he acts. And,
2. The want of prudence and management in the fool, who has no restraint on his passions, and no rule or guard upon his tongue. The right hand and the left are used in Scripture to express good and evil. The wise man is always employed in doing good; the fool, in nonsense or evil.

A (a) wise man's heart [is] at his right hand; but a fool's heart [is] at his left.
(a) So that he does all things well and justly, where as the fool does the contrary.

A wise man's heart is at his right hand,.... This is not designed to express the direct position and situation of the heart of man, wise or foolish, which is the same in both; and which, according to anatomists, is in the middle of the body, inclining to the left side; but the understanding and wisdom of men, as Aben Ezra observes; which, with a wise man, is ready a hand to direct and assist him in any affair; and which under the influence of it, he goes about with great readiness and dexterity, and performs it with great ease and facility, without sinister ends and selfish views; it inclines him to pursue the true way to honour, heaven, and happiness, which lies to the right; to seek things that are above, at the right hand of God; and, in all, his honour and glory;
but a fool's heart is at his left; he is at a loss for wisdom and understanding to direct him, when he has an affair of any moment upon his hand; which he goes about in an awkward manner, as left handed persons do, and has sinister ends in what he does; and he is to every good work reprobate and unfit, and seeks earth and earthly things, which lie to the left, and in all himself. The Targum is,
"the heart of a wise man is to get the law, which was given by the right hand of the Lord; and the heart of a fool to get the goods of gold and silver:''
so Jarchi,
"his wisdom is ready to incline him (the wise man) to the right hand way for his good; but the heart of a fool to pervert him from it.''
The ancients (o) used to call things wise and prudent the right hand and things foolish the left hand.
(o) Suidas in voce

(Ecclesiastes 2:14).
right--The right hand is more expert than the left. The godly wise is more on his guard than the foolish sinner, though at times he slip. Better a diamond with a flaw, than a pebble without one.

A double proverb regarding wisdom and folly in their difference: "The heart of a wise man is directed to his right hand, and the heart of the fool to his left. And also on the way where a fool goeth, there his heart faileth him, and he saith to all that he is a fool." Most interpreters translate: The heart of the wise man is at his right hand, i.e., it is in the right place. But this designation, meant figuratively and yet sounding anatomically, would be in bad taste
(Note: Christ. Fried. Bauer (1732) explains as we do, and remarks, "If we translate: the heart of the wise is at his right hand, but the heart of the fool at his left, it appears as if the heart of the prudent and of the foolish must have a different position in the human body, thus affording to the profane ground for mockery.")
in this distinguishing double form (vid., on the contrary, Ecclesiastes 2:14). The ל is that of direction;
(Note: Accordingly, Ecclesiastes 10:2 has become a Jewish saying with reference to the study of a book (this thought of as Hebrews.): The wise always turn over the leaves backwards, repeating that which has been read; the fool forwards, superficially anticipating that which has not yet been read, and scarcely able to wait for the end.)
and that which is situated to the right of a man is figuratively a designation of the right; and that to the left, a designation of the wrong. The designation proceeds from a different idea from that at Deuteronomy 5:32, etc.; that which lies to the right, as that lying at a man's right hand, is that to which his calling and duty point him; השׂ denotes, in the later Hebrew, "to turn oneself to the wrong side."

Heart - His understanding is always present with him and ready to direct him. He mentions the right hand, because that is the common instrument of action. A fool's - His understanding is not effectual to govern his affections and actions.