Is it true that if you try not to stutter for 21 days, you will never stutter anymore after that?

Is it true that if you try not to stutter for 21 days, you will never stutter anymore after that? I heard that doing anything for 21 days, will make a habit forever until you change it someday. So, talking fluently for 21 days. Maybe to don't go anywhere where you feel anxiety and be in your comfortable zone for 21 days and talk, talk & just talk fluently. Will it really help?