Even if there isn't an underlying problem, the only real way to change a habit is to replace it with a new one.

I have noticed that usually people who make it their mission to stop doing a thing are replacing that thing with the mission itself. This strategy is always bound for failure, because the moment it starts to work for them is the moment they end the mission. This is when, instead of reevaluating their strategy, they punish themselves for the failure to not do. The cycle repeats, and the person spirals into rumination about their stress.

I didn't just stop biting my nails. I started trimming them instead.