How long does it take to form or break a habit? I.e bite nails, thinking positive, suck thumb?

making a behaviour automaticHow long does it take to form or break a habit? I.e bite nails, thinking positive, suck thumb?
I know this sounds stupid but i heard it takes 21 days, or three weeks if you go without doing the behavior





i don't think that applies to drugs or alcohol, just basic habits like the ones you said.





I think i hears it on Dr. Phil.





-Dix