Perhaps unconsciously making a deal with your addiction?
I was a daily drinking for over 30 years. Six months sober was an amazing and unbelievable milestone for me. Yet I started thinking about drinking...thinking once every 6 months was better than daily. A nice little compromise I thought, 363 sober days out of 365.
But I didn't drink at my six month mark. Who knows where that first drink would have led. Maybe ten years of drinking, which followed one of my earlier "compromises" to sobriety.