It's a nice thought that things that happen in the past, stay in the past. The issue is that it's not true.

Trauma often creates implicit, nonverbal memories that can't be fully processed just through talking about them.

Some types of trauma that happens in relationships, interpersonal traumas, are sometimes overlooked or minimized. This may be in part due to

Over time the stress from witnessing accidents and deaths, responding to emergencies, hearing the details of people's worst moments...