From The Power of Habit: Why We Do What We Do in Life and Business by Charles Duhigg:

When people join groups where change seems possible, the potential for that change to occur becomes more real. For most people who overhaul their lives, there are no seminal moments or life-altering disasters. There are simply communities–sometimes of just one other person–who make change believable…

“Change occurs among other people,” one of the psychologists involved in the study, Todd Heatherton, told me. “It seems real when we can see it in other people’s eyes.”

…Belief is easier when it occurs within a community.