We have to go to school, sit quietly in class, listen to the teacher, perform the exercises, do our homework, etc etc. This is when we get into the habit of habits. The trouble is, this predictable repetitive lifestyle is not something the human brain was originally designed for. We are tremendously adaptable creatures and seem able to adapt to almost anything, but that doesn't necessarily mean its a good idea. The most fundamental change in human society occured when we evolved from being hunter gatherers to being farmers.
Hunters have distinctly different requirements to farmers.
A hunter needs to be continually aware of his surroundings, so his attention will quickly focus on anything that may be a threat or opportunity. As a hunter, novelty, constantly monitoring the surroundings, and creativity are the most important requirements for success. He needs to be able to sustain a steady, even level of effort, even with no apparent clear gain in the immediate future. Our brains learned to cope with life as a farmer by producing more dopamine. Some theories suggest that dopeamine developed as a survival technique for seige like situations.