Established habits demand little conscious effort, but creating a new habit is hard work. Psychologist Phillippa Lally of University College London asked 96 undergraduates to form a habit in 12 weeks by repeating daily a healthy behavior, such as drinking a bottle of water with lunch. Published in the October European Journal of Social Psychology, her results suggest that habits take much longer to form than researchers previously thought (an average of nine and a half weeks and potentially as long as several months), but missing one or two days of repetition will not impede the process.