Sometimes it helps to think about the human brain as a computer. Environmental data gets feed into the system through our senses. The system initiates numerous tasks gear towards interpreting, manipulating and querying new information and storing it in memory. It then determines the next action and the cycle repeats.
One of the tasks is to check your memories for similar experiences looking for matches and make you aware when it finds one through thought, emotion or a gut feeling. A match is good and you get a small reward when you find one. It means you’ve encountered this experience before and therefore have a workable solution in place. This is always true because if you encountered it before what you did before allowed you to live to encounter it again. Deferring to the previous solution is going to decrease mental effort because it requires less thinking and the physical behaviors have already been performed by the body. It’s probably going to feel somewhat pleasant and it is the fastest way to the next action.
You wouldn’t want it any other way in the primitive world we inhabited 15000 years ago. The world was so dangerous that you needed single trial learning because you very rarely got a second chance. You need to be alerted when the watering hole has the same look it had right before the alligator jumped out and killed someone in your tribe because recalling this will keep you alive.
It’s a perfect system for dealing with emergency situation and situations were your previous action was the most effective action. It can be dangerous if the pattern isn’t one that works for us, for example conflict avoidance with a partner or disregarding someones opinion because of a physical characteristic. When a response becomes automatic without being vetted for relevance and appropriateness based on your current understanding of the world you may run into problems.
Given that there is a survival reason to do what you did the last time, you may benefit from taking a moment to make sure your action is going to be your best action. If you are doing it simply because it is easy, you might want to stop doing that if you want to get more out of life. Remain diligent for 30 days and you’ll likely find that you are happier and more productive.