Habits are those things that the brain learns to do without conscious direction. For instance, an accent or speech mannerism is usually habitual. Since speech is so useful and common, we can't afford to constantly be thinking about the how of speaking; we must concentrate on what we actually want to communicate. Therefore, the brain learns to do all of these things without conscious intervention.

This is a very Good Thing. Imagine if you had to think about how to walk, speak, eat, move, etc. We would get so bogged down in planning each muscle contraction and release that we would never be able to do anything

However, habits can carry ill effects as well. If you train yourself to do something incorrectly (like walking with your feet at an odd angle or hunching your shoulders when you sit) you will subconsciously do these things incorrectly. This can lead to poor performance and even injury.

Additionally, habits are meant to be permanent and can be quite difficult to replace if they are incorrect. The best approach is to "interrupt" the brain forcefully while it is in the process of performing its learned operation. Doing this consistently can be fruitful in replacing bad habits.