The brains intent is survival and procreation. In striving for these it defaults to and will take the most immediately, energy efficient, choice.
The brains way of increasing the odds of survival are to repeat behaviours that it has been successful with in the past. “X stimulus led to y reaction from me. I am not dead, therefore y worked successfully.”
The mind’s/brain’s way of promoting past behaviours is taking the most energy efficient pathway. (Actually it’s more of a bidding system but the result is the same and this is adequate for the purpose of this explanation).
“Neurons that fire together wire together.”
Nature is lazy, and as animals, so are we.
Generally in physics things always follow the path of least resistance. So next time someone says you’re lazy tell them it’s natural (and they will presume, for no good reason, that “natural”, equates with good or healthy or appropriate).
When we receive a stimulus electrical / chemical reactions take place in certain pathways of neurons. The more a pathway is used the less resistance is on the pathway. Think of walking back and forth through a corn field or even dense jungle – the more people who do it the less resistance and difficulty is involved as each person clears out a little more. As more people walk back and forth, most of them taking the easiest path they can find a particular path true the vegetation begins to appear. And as people continue walking back and forth because this path is slightly easier than going through the rest of the vegetation more people begin to use it. And the more people use it, the more clear and flat and defined it becomes, and it gets even easier to use and even more people use it. Until you have a path through the vegetation. As a group the people move faster and use the path even more often. The faster and more frequently they’re moving the quicker the pathway becomes even clearer and the faster they can move again. This is called habit.