Emotion is a physical event. When it is not allowed to finish, the body keeps the unfinished part.
Every emotion is a full-body response: a surge of chemistry, breath, muscle, and impulse: to cry, to speak, to push away, to run. When that response can complete, it passes through and the system resets. When it cannot, because you had to stay composed, because it was not safe, because you were a child and there was no one to receive it, the response does not disappear. It gets interrupted, and the nervous system stores the unfinished pattern as tension, held breath, and a low permanent bracing you eventually mistake for your personality.
That is what people mean by “stored emotion”. Not a mystical deposit, but an interrupted physical response the body is still waiting to finish. Releasing it is less about understanding why (most people already understand why) and more about giving the body the conditions to complete what it started.