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.
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 John Truby’s word ‘ghost’ 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’.