Way a long time ago, back when the world was still black and white (color tee-vee not yet being affordable), we used to do cool 'speriments in science class.
We did this one with planaria, which are freshwater flatworms.
We were introduced to the theory that these worms could regenerate lost body parts. In fact, the theory went, you could cut them in half and each half would regrow the missing part, leaving you with two complete flatworms!
I remember doing this experiment. Before we cut the worms the teacher also informed us that the "eyes" on the head of the worm were not like our eyes, but photo-receptive cells. The worms couldn't "see" like we see, but they could detect light. Since they like to live in dimly lit ponds, they would react to bright light by moving away from it. They would also, the teacher said, move away from things that touch them.
So we shined lights on the little worms and they moved away from the light. And we poked them with probes, which also caused them to move away. Finally, we cut them in half, than checked on them every morning. Sure enough, over time, each half of our planaria regenerated its missing part and became two complete and independent flat worms.
In addition to lacking eyes, arms, legs, hands, feet, noses, etc., planaria also differed from us in not having a brain and in not having the ability to think and reason. They existed as living beings, but they didn't make plans or decisions or even politely ask children to not shine lights on them or poke them or cut them in half. They couldn't do that. No brain. No cognition. All they could do is react to environmental stimuli.
And regenerate lost parts. Which was cool.
Now I have a brain and cognition. But sometimes (a lot of the time) I react rather than reason. Even though I have a brain.
It's good to be able to react without thinking. Much better to snatch my fingers away from something painful than to have to sit down and do the math before removing my digits from whatever is damaging them. I've only got eight fingers and two thumbs after all.
Sometimes, though, it's better for me to think things through before proceeding. If I decide I want to fly it might be better to figure out a way to get on an airplane rather than just jump off a cliff and hope I can fly without an airplane.
Sometimes it's better to stop and think before clicking the button to purchase the "magic flying suit, no airplane required."
Sometimes it's better when I double check my assumptions. When I react instead of reason, I'm kinda making myself into a planaria. But as a human, I lack the ability to regenerate lost parts.
If I cut off my head, it won't grow back.