The climax of a story is the turning point. The action or plot builds to this key event or choice. Everything after the climax is generally just the resolution or result of that event or choice. ("It's all downhill from there.") If the story continues too long after the climax, it often feels like it is "dragging". But if it doesn't provide that additional resolution, the reader can be left feeling "what just happened?!" -- sort of like the shock that happens in real life after something startling occurs.