Gemara: What is the background behind the prohibition on a shoe called sandal hamesumar? Shmuel said: there was a decree [made by enemies], and people were hiding in caves. The people in the caves agreed: "Whoever comes in, comes in; and whoever leaves, leaves." The shoe of one of them was turned around, so that they thought that one of them left and was seen by the enemies who were now attacking. They started pushing each other and killed more of each other than the enemies killed of them.
Ein Ayah: The source of falling is the collapse of the spirit, as the intellect leaves him and his imagination sinks. It is as the pasuk says: "Israel abandoned goodness; the enemy will pursue" (Hoshea 8:3). The imagination lowers a person and the nation as a whole to a ditch, i.e., into dense materialism and its ugly and lowly tendencies. It is not the external perceptions that is dominant in its midst, as the pasuk says: "To the action of Hashem they did not look, and they did not see the work of His Hand" (Yeshaya 5:12). External imprints have their impact according to their natural ability to give light. They do not extend to revive the spirit and to spread light to the intellect and one’s personal attributes. [This is what the gemara means by that which comes in, comes in, and that which leaves leaves.] The results are similar to what one would expect. There is a lowliness of the spirit, fear of the enemy, hiding in a cave, and a lowly decision based on continual decline, due to fear of the enemy.
Imagination, which is from the outset the factor that causes people to abandon Hashem and the paths of straightness, itself becomes the medium through which punishment comes. It deepens the feelings of evil and increases the weakness of the spirit to the greatest degree. When something changes even in the slightest, it causes the whole world to turn around for him. Imagination is not like intellect, which can handle each new situation and conception throughout physical and spiritual life and use its strength to lead one in the proper and righteous path. In contrast, imagination is spoiled by a small wind; one murky idea can summon up many bad feelings and consequences. Thus, when one shoe was turned around, frightening and desperate decisions were made, and they believed that the enemies discovered them and were attacking.
Not only does the decision one comes to based on imagination tend toward bad, decline, and despair, but it actually causes the ruin of the person with the imagination. It does not allow the individual and the community to notice their situation and return to a higher level by using the intellect and morality to elevate them over the situation of lowliness and fight off the situation of difficulty. Rather imagination increases commotion and inner enmity and ends the glimmer of hope that the powers can be summoned to survive. This is the horrible tragedy of a person who causes more destruction to himself than any enemy. It all starts when he is removed from the light of the pure intellect and the lofty aura, the light of the G-d of truth. It causes him to embrace fleeting mistruths and improper personal attributes that stem from a bad imagination. It concretizes the bad thoughts with thick mud and with irremovable nails. "Your evil shall oppress you, and your iniquity will rebuke you; you shall know and see that it is bad and bitter that you left Hashem your G-d, and My fear is not upon you" (Yirmiya 2:19). Instead of a thought-out fear of Hashem, which puts the mind at ease and fixes every group that lost its moral content, the bad imagination creates extreme, purposeless fear. This pollutes the mind and increases commotion and self-destruction beyond what any enemy could accomplish.