As an ex-smoker and ex-sugar addict, I'd say quitting smoking is harder. But I did quit smoking cold turkey, but eliminated sugar gradually. First by replacing it with sweetener and then reducing the sweetener over time. None in coffee, only drink soda water, bubble water, seltzer water, whatever it is called in your neck of the woods. And I do mostly carnivore diet, so little to no carbs and specifically sugar.