A wise man's heart is at his right hand; but a fool's heart at his left. There is here no reference to the classical use of right and left, as ominous of success and disaster, which is never found in the Old Testament.
The right hand is the place of honor, the left of inferiority, as a matter of fact, not of superstition and luck. The symbolism is intimated in Christ's account of the judgment (Matthew 25:31, etc.).
But in the present passage we should best paraphrase—The wise man's heart, his understanding and sentiments, lead him to what is right and proper and straightforward; the fool's heart leads him astray, in the wrong direction.
The former is active and skilful, the latter is slow and awkward. One, we may say, has no left hand, the other has no right. To be at the right hand is to be ready to help and guard. "The Lord is at thy right band," to protect thee, says the psalmist (Psalms 110:5).
The wise man's mind shows him how to escape dangers and direct his course safely; the fool's mind helps him not to any good purpose, causes him to err and miss his best object.