If our mind is just a machine that functions in accordance to available chemicals and stimulus then purely existing in the world will cause cognitive changes.

Your nutrition and available chemicals in your body changes over time, depending on what you consume, what kind of air you inhale, what kind of organisms are living inside of you. All these effect how your brain works.

Everything we see, hear, smell, touch, taste, is a stimulus that the brain will respond to. Even patterns and waveforms of light can change how your brain acts. Pretty much everything that exists is affecting how our brains work. We just ignore most of it.

The agents of change are even more obvious in a case of breaking an addiction. The experiences of being an alcoholic is constantly feeding into memory, each experience is different, and complicates that system. Even simply existing they will be put under the stimulus of withdrawal in some environment, the brain will react to that also. They may here a friend or family member's opinion on their addiction, they may read a book, see an ad online, they may see someone in public that makes them think a certain way, they may see a painting, or a building, or a piece of cheese that for some reason connects in their mind some action for change. It's never just one thing either, there's an unfathomable amount of stimulus happening all the time, and it can all work towards a cumulative effect like deciding to break a habit.

Further environmental factors, based on your brain, will influence whether you do or don't succeed. But those factors could be anything and everything.