The commonly stated “it takes 21 days to form a habit” is a myth. Researches indicate that habit forming doesn’t have a magic number, and repetition along is not enough to form habits.
The 21 days myth is based on a misinterpretation of a statement made in best seller behavior changing book Psycho-Cybernetics. In the book, the author states his observation that people need “a minimum of about 21 days” to form habits. Later interpretations dropped the word “minimum” and failed to mention that “21 days” is a personal observation rather than a scientific finding.