It's an expression that explains behavior. It compares the human brain to a computer or machine. If you open up either of those, you will find electrical wires inside them, right? These wires allow the machine or computer to operate correctly. With humans, our brains function with the aid of things like axons and neurons. When a person uses this phrase, they are saying that the person's brain makes them naturally inclined to have certain thoughts or behave in a certain way. It's just how they are by nature. I hope this answer helps! Let me know if you would like some examples or if you understand now. :-)

The question can only be accurately answered if you supply the full context, the surrounding context and also the title of the text/book article etc. All other answers although correct and useful, are jumping to conclusions as to the title and the context. The contest or subject of the text could equally well be about an individual with a brain problem. In which case depending on the style of writing. "The brain" could or may be an individual persons brain or a person suffering from a specific disease. It may even be referring to an insects or an animals or even an aliens brain. Without the context we can only guess.

It means the way you think about handling a situation, problem or task.