A person who chooses a life of idleness and inaction ultimately brings about their own ruin. An unwillingness to put in effort sets off a cycle of self-destruction, where an individual drains their own resources until nothing remains.
The primary approach among commentators views this dynamic through a practical, economic lens. A foolish person is seen as lazy and completely devoid of ambition [אבן עזרא]. By simply folding his arms and avoiding any productive labor that could provide a living [מצודת ציון, מצודת דוד, אבן עזרא, ביאור שטיינזלץ], he sets himself up for extreme poverty. The resulting self-destruction is compared to a person eating his own flesh, serving as a metaphor for severe starvation. Without a source of income or new food, he uses up whatever little he has left until his body wastes away, starving as if he is literally consuming his own body out of absolute destitution [מצודת דוד, אבן עזרא, ביאור שטיינזלץ]. Beyond physical hunger, this also reflects a mental state of deep frustration, where the individual emotionally eats away at himself over his own failure [ביאור שטיינזלץ].
In contrast to the physical explanation, other commentators interpret this path of ruin on a spiritual and moral level. From this viewpoint, the fool is not merely lazy, but wicked [רש״י, תעלומות חכמה, צאינה וראינה]. His folded arms represent a deliberate avoidance of Commandments and good deeds [תעלומות חכמה], as well as an abandonment of Torah study [תורה תמימה]. Instead of working honestly, he chooses to survive through theft [רש״י, צאינה וראינה].
The devastating consequences of this spiritual laziness become fully apparent on the Day of Judgment and in the World to Come. The present world is compared to the day before the Sabbath, a time meant for preparation and gathering merits, while the World to Come is like the Sabbath itself, the time to experience the reward. A person who failed to prepare is left with no spiritual reward to enjoy [תעלומות חכמה, תורה תמימה]. When this wicked individual sees the righteous and those who dedicated themselves to Torah sitting in honor, while he is condemned to remain among the wicked, he is overwhelmed with profound sorrow. Gripped by the agony of regret, jealousy, and frustration, he grinds his teeth and torments himself to such an extreme degree that it is as if he is eating his own flesh from the sheer pain [רש״י, תורה תמימה, צאינה וראינה].