Here's an example: You see a tiger in the forest. Your eyes send that signal through their nerves to the brainstem, which makes your stomach tight and activates your legs to run away. The tight stomach and running legs then send their signals of movement and clenching back up through to limbic system ("I'm scared!") and the neocortex (your conscious brain, "I'm running away from the tiger!") to tell it to run. Because all of this happens so fast, our experience is this: We saw the tiger and therefore we're scared and are running away. That's not really what's happening under the hood, we're scared BECAUSE we're running and have a tight gut, the tiger was just a trigger for the brainstem/gut/legs. Makes sense?