One way of overcoming one’s nature is through intense Kabbolas Ol, the Previous Rebbe writes:
You ask me for a solution to your natural inclination to constantly tell jokes. You cannot restrain yourself, and even after you feel guilty over it, all your resolutions to abandon the way of constant joking are not effective for longer than several days.The centre of the Avodah of Chassidus is improving and refining our character traits. There are different ways of going about this.
Your soul will only be saved though Kabbolas Ol—by placing a bit and a rein on your mouth, not to speak anything until you have considered carefully whether to speak or be silent. This is what you should do daily: when you wake up in the morning, place a bit and a rein on your mouth, and do not divert your attention from it the entire day, until you sleep.
The task of Kabbolas Ol in general, and for the purpose of overcoming a natural trait to which one has become accustomed in particular, is extremely difficult. However, once one realizes that this is needed in order to save one’s soul, one ought to compel oneself to overcome the test with tremendous might.
At first it will be very difficult for you, but then Hashem will help you, and from day to day the struggle will become easier, until, with the help of Hashem you will eliminate the base trait from within, and reach a state of spiritual illumination.
Igros Kodesh Admur HaRayatz, Vol. 4, p. 355.
Sometimes one should refine a character trait slowly and painstakingly, and not try to eradicate it all at once by taking upon oneself to make an extreme, herculean effort. This is the approach expressed in the verse, “Little by little I will banish him” (Shemos 23:30).
In other cases, however, that approach will simply not work, for the person will see that he finds himself in a vicious cycle of resolving to change, changing briefly, and then reverting to his old ways, back and forth, with no end in sight. Then the only way to deal with the negative character trait is to go “cold turkey”—to resolve with extreme determination to abandon that trait entirely, and be tremendously vigilant.
How does one know when to follow the slow approach and when to follow the cold turkey approach? Based on this letter, it would seem that when one is dealing with a bad character trait that is wildly out of control, and other solutions have not worked, it’s time to follow the latter method.