To be reasonable, you must be able to reason. Our ability to reason is what makes humans humane. And when we abdicate our frontal lobe cortex’s responsibility to interact as adults with others, we devolve into our reptilian brains. And nothing good happens in the Jurassic Park parts of our perceptions.
The brain is one of the busiest (second only to the liver) and the laziest organs in our entire body. Our brains tend to focus on things which make it feel good, keeping us in our comfort zone. If your brain is left unstimulated, it results in a condition known as lame brain or dull skull, both of which fall into the untremendous category.