The Dark Side Will Make You Forget

The Dark Side Will Make You Forget is the TV Tropes-popularized term about warning where turning to the dark side, either by one's own choice or corruption from outside force, is not something to be underestimated as it would made one to forget his/her true self.

A hero or other good guys may had to take a morally grey action (which decision deemed neither bad nor good) to solve his/her problems at hand, but it must be done wisely along with some consideration as they would likely lost their way in the process and unknowingly become evil until it's too late. As if losing oneself to the darkness already bad enough, dwelling in it for too long might resulted whatever goodness in their hearts to deteriorate to the point they eventually embraced the path of villainy and even not hesitate to cross Moral Event Horizon

A character who turned to the dark side due to ignoring this warning may be sympathetic, as they are either victim of corruption that turned them evil in the first place or possessing weak heart that vulnerable to even unexpected source of corruption like higher power/status. While they may have good intentions in committing morally questionable decisions, the longer they dwell in darkness through it, the more they forget their original dreams and goals. Those who still have redeemable qualities can be stopped before becoming full-blown irredeemable villain through their own conscience or through reasoning with his/her allies/loved ones/families, though they may still follow the dark path or chooses to turned around.
 * Choosing bad/selfish choices: The hero/heroine is given clear choices over the course of his/her life, but he/she tend to choose negative ones (either in form of taking selfish choice or sought the assistance from villains) that worsened their reputation over time and unaware that he/she slowly become as worse as those whom he/she fought against. For instance, Cole MacGrath can slowly become evil the more he choose selfish decisions.


 * Willing to follow/succumb to evil influence: The hero/heroine is fully aware with the risk of malevolent corruption/negative influence that would made him/her evil, but willing to submit to it. Example: Nimue, consumed by rage and hatred towards Vortigern for killing her family, ended up killed him in cold blood in spite of Merlin's protest, resulting her corruption and transformation into Dark One.


 * Lack of strong will to overcome corruption from power/influence they vulnerable with: The hero/heroine is put into the situation where he/she had her psyche and conscience figuratively or literally struggled against malevolent influence that can turm him/her evil, ranging from brainwashing or corruptive substance that can corrupt both body and mind of those who touch it (which can be either scientific or supernatural in nature or both). But to make the situation relevant for this article, the hero/heroine's conscience and will to overcome the corruption would be put into a test: The hero/heroine would try his/her best to resist the corruption for a long time, but because he/she failed to rid the corruption before it's too late, he/she eventually become evil that had neither his/her friends succeed to reach for him/her, they had to put her out of her misery. The example would be Garmadon, whom eventually succumbed to corruption from Great Devourer's venom after keep it at bay for a long time, and eventually able to redeemed himself once the corruption cured through exorcism by his son Lloyd.