There are various words to describe the event from a main character’s past which holds them back in the present: the fatal flaw, the psychic wound, the ghost. I’ve even heard ‘scars’.
A character becomes their scars. That’s not to say they’re defined by them, but their responses to them are.
Fatal flaws aren’t always fatal and suggest they tend to be inborn. Fatal flaw refers to what I prefer to call the psychological weakness, and the ghost is a bit different.
‘Psychic wound’ is good, but other people use the word ‘ghost’. (John Truby, Karl Iglesias.) This is even better because I can visualise this thing as an alter-character following the main character around, actively getting in the way of their goals. However, ghosts refer to supernatural creatures, so let’s stick with ‘psychic wound’.
Most often, the Ghost involves traumas such as abandonment, betrayal, or a tragic accident which leaves the character permanently injured or disfigured, or causes guilt if the character feels he has caused another’s death. It can also be the death of a loved one. Basically, any traumatic incident that created a sense of loss, or a psychological emotional wound. […] The difference between Backstory and Ghost is that the first molds the character’s personalty, whereas the latter is still an open wound which haunts the character in your story and affects his inner need. Both, if interesting, can add emotional complexity and fascination to your character.
— Writing for Emotional Impact by Karl Iglesias
Notice Iglesias mentions injuries and disfigurements. A disfigured character is a trope of yore, and modern writers need to be careful about that one. In these more enlightened times we know that a disfigurement or injury or missing right hand does not actually say anything about that person at all, but earlier stories conflated physical wounds with evil and mal-intent.