I remember being little and encountering things that I might react to very differently today. At the time, there wasn't always a big emotional response. I didn't necessarily know how to feel about what happened. As I got older, some of those same situations began to mean something else to me.
Experience changes interpretation
We learn by living. We make decisions, see what happens, and carry those outcomes into the next situation. Sometimes the event stays the same in memory, but the meaning we give it changes. Maybe the feeling isn't missing forever. Maybe we haven't developed the perspective that makes it understandable yet.
When the past makes the next decision
An emotional response can shape a decision, and that decision can create another experience that reinforces the emotion. The loop can become familiar enough that we mistake it for the only available choice. Learning to recognize that loop doesn't erase the past. It can give us more room to decide what happens next.
Still figuring it out
I don't think this explains every emotion, and I don't think anyone needs a perfect theory to notice something true about their own life. What I do know is that understanding can arrive after the experience. Sometimes you don't know how to feel yet.