At what point does an action change from something you do sometimes to a habit?

At what point does an action change from something you do sometimes to a habit?

At what point does an action change from something you do sometimes to a habit? At what point does a habit become an addiction? Do those same points exist in reverse and are they in the same spot? Is this more of a medical question or maybe physiological? Is it a mental change you make (whether you know it or not) or a physical change? Why is it so hard to break but so easy to make worse?

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