in my situation, i remembered some trauma in childhood while my closest sibling did not, claiming it never happened. i also had other trauma that she did not and as a result did not cope as well overall compared to her. she was affected to a lesser degree and could just go on with things.

the difference between us was personality types, ability to leave the house/situations, etc. and overall resiliency. i was the youngest, quietest, smallest, more cautious/fearful, etc. she was more outgoing, outspoken, etc. and would stick up for herself. she was able to go be with friends more often than i was.

i also had two older siblings who seemed overall to do better than me. i mean, they all have had their own issues from various things, but their ability to cope was different than mine. i do not know either how early they experienced trauma in life, so maybe that makes a difference too. mine started around four or five years old, so when my siblings were older than me.

as for dissociation or forgetting trauma/difficult things being positive, it can as it helps a person get through trauma/overwhelming situations. it only becomes negative when it impacts a person's life in a way that affects their functioning.

i would not say that my one sister necessarily experienced dissociation (but maybe to a mild degree) related to the trauma we went through together, but more plain old forgetting maybe because her way of dealing with things overall (as well as my older two siblings) is out with the old/negative and in with the new with the ability to just push things out of their awareness willingly...and also, if something isn't important to them, they just won't think/feel/talk about it, etc. so, if they aren't affected like i am where memories/negative feelings, etc. are intrusive or cause issues with functioning, the way they are able to function and live is different than the way i live. for whatever reason, they were resilient in a different way.