They have become such a normal activity that the brains are no longer consciously noticing them. Let's be honest - you may be fighting a dependence on alcohol or drugs, nicotine, caffeine or sweets for that matter. Habits develop without you noticing the consequences they are having on your life. Then when you finally see the results and decide to change, they have you in a trap. You want to quit, but you can't .
Some habits are stronger than others.
But they were developed in the same way - by repeating the same actions over and over. Once you recognize what habits are and how you got them in the first place, you can see that it's possible to change them. You must want to change. Change is disturbing to us. It is in human nature to resist change.