I've worked with trauma/PTSD and c-PTSD and this is the way I describe it.
When something bad and/or unexpected happens – either as a single trauma or a series of linked events – a part of the mind takes on the job of figuring out exactly what happen, why it happened and (crucially) what our role was in the event. This isn't to punish or torment us but to stop that particular thing happening again – it's a protective mechanism to prevent further hurt, either physically or mentally.
That will be resolved quickly if (for example) we admit were texting when the car accident happened, or the abuser confesses and is punished, but some things are just so random or unexpected that there's absolutely no way of predicting them, preparing for them or avoiding them. It is just 'one of those things'.
However that bit of your subconscious doesn't get this message and carries on relentlessly looking for clues – hence the flashbacks, intrusive thoughts, nightmares that are often part of trauma and (for you) the "why me?" for single traumas and "I MUST be somehow to blame" when the same thing keeps happening in the case of childhood abuse (you never are to blame).
Once that part of your mind understands that there isn't, and never will be, a satisfactory answer it will stop, because it's a fruitless exercise which is detracting from your happiness in the present day. You won't forget what happened but the emotional link will be broken.