The first occurrence.
For he sees wise men die; likewise the fool and the senseless person perish, and leave their wealth to others. Psa 49:10
The primitive root.
Strong’s H3684 keciyl, a concrete noun meaning, “foolish complacency,” from Strong’s H3688 כסל kacal, a primitive root meaning, “to be fleshy, fat, or inert.” The ancient pictographs are kaph + sin + lamed.
kaph כ, ך = the open palm, thus bend, open, allow, tame
sin ס = the thorn, thus grab, hate, protect
lamed ל = the shepherd’s staff, thus teach, yoke, to, bind
The parable the pictographs are telling is of covering (kaph) which protects (sin) the staff (lamed), or male reproductive organ; i.e. loins, according to the Ancient Hebrew Lexicon, thus, fleshly, fat, or inert, as when the flesh covers a man’s loins.
The idea of complacency comes from the loins acting as the seat or root of confidence; first, as deriving self-worth and self-aggrandizement from the flesh, and second, as a metaphor for fleshly or worldly strength. The over-confidence thus generated leads to complacency, laziness, or inertness.