We tend to take for granted things that are natural. And because they are natural, we simply do not think much about them.
Take for instance our digestive system. Just because it can digest food for us, sometime we may feel guilty of just swallow (gobble) food with little chewing. This is not healthy for our body. We are letting the stomach do the extra work to digest the food, robbing the blood from flowing to our brain when we need to do the thinking.
Another example is our eyes. We can work or play with ease because of our ability to see. Because of this, most people would tend to care less about their eyes. They do not give them sufficient interval rest, such as looking at a far distant every 20 minutes of work.
The same goes to stretching our brain and not giving it much interval rest. It is as good as saying that we are forcing our mind to stay at the conscious level and does not want it to go into the subconscious level.