The bad habit usually has a cue: boredom, a certain room, a certain time. Change the cue and the habit gets weaker.

Habits are triggered before you decide anything, and the trigger is always specific. It is not a general weakness; it is boredom at a particular hour, or one chair, or the ten minutes after a certain class, or one person’s company. The reason this matters is that you almost certainly do not know your own cue.

So spend three days finding out rather than guessing. Each time the habit fires, write down the time, the place and who was there. Three days is usually enough for the pattern to be embarrassingly obvious, and then you have something you can change.