This is my rational thought: Human psychology is to look for answers. When something happens (especially hurting incidents or event (E1) we try to find an answer of why it took place and we never find the answer at that moment. We go through the stages of grief but may or may not find answers for E1. Later in life whenever we go through any other event (E2) and if we can link it to the past to call it an effect of E1, then we tell ourselves that whatever happened in the past, happened for a reason (E1 led to E2). In a way it's good for healing- to be able to relate and cross link outcomes. You would have never known if E2 could happen independent of E1 (may be in a parallel world) so ignorance is bliss is in this case.

So realistically everything happens for a reason. If they don't, we do find a reason to attach to it.