Mine was smoking. Also did it cold turkey, with sugar-free mints and chewing gum.
I don’t know the habit you’re referring to nailit but I guess my edict/rules for stopping would apply to a lot of things.
First, I got rid of everything to do with fags. No matches, lighters, ashtrays and no ‘emergency’ pack of 5 under the sink!
Second, my mantra was: no thanks, I don’t smoke. That was in reply to every time I was offered one.
Third, it was a case of reaching small targets each time. First aim was to get to 10 hours, then a full 24, then 48. After that it was to aim for 3 days, then 5, then 7, 10 and so forth. At 7 I gave myself a little reward. Could be a cream cake, new shirt, trip to a restaurant. That gave me a sense of inner smug satisfaction that I was no longer ruled by the Melvyn’s, it’s all psychological.
25 years now, must have saved a fortune.
Hope that helps, good luck in kicking whatever habit it is you wish to break.