Human nature is highly sensitive and easily shaped by its environment and habits. The company a person chooses to keep is never merely a social preference; it is a fateful decision that determines their future, with the power to either pull them toward good or drag them down into bad [אמרי דעת].
A person who constantly seeks out the wise and actively pursues their company is guaranteed to become wise [רלב"ג, ביאור שטיינזלץ]. At first, this person is not considered an equal to the wise, but rather someone who simply tags along. Because acquiring wisdom demands significant effort, it is better to act as a follower, trailing behind great people until their fine character traits naturally take hold [אלשיך, מלבי"ם]. Growth happens both through active effort, such as observing their actions, accepting their moral guidance, and learning from their insights [רלב"ג, מלבי"ם, עמנואל הרומי, מצודת דוד], and through the simple, positive impact of just being in their presence [ביאור שטיינזלץ]. Ultimately, God rewards this dedication by granting the person the greatest possible good, which is wisdom itself [רלב"ג].
On the other hand, there is a severe danger in connecting with fools. The primary approach among commentators is that this refers to a person who befriends fools and becomes their companion [רש"י, אבן עזרא, מלבי"ם, מצודת דוד]. Unlike the pursuit of wisdom, which is difficult, surrendering to foolishness and chasing physical desires is fast and effortless, meaning a person can instantly form a close bond with fools [מלבי"ם]. A second approach understands this connection as an act of leadership, referring to someone who appoints himself as a guide over fools. Even if his goal is to fix their flaws and steer them away from bad behavior, he will ultimately be corrupted by their influence, reaching a point where he actually needs their leadership [אלשיך, מלבי"ם, ביאור שטיינזלץ].
The inevitable result of any connection with fools is utter brokenness and destruction [רש"י, אבן עזרא, מצודת ציון, מלבי"ם]. Whether a person joins them as a friend or tries to be their leader, he will eventually break and be lost. He will learn from their bad deeds, his stability in the world will be shaken, his soul will suffer, and he will ultimately face the punishment reserved for sinners [רלב"ג, עמנואל הרומי, מצודת דוד].