If you wish to be stripped of your vices you must get right away from the examples others set of them. The miser, the swindler, the bully, the cheer, who would do you a lot of harm by simply being near you, are actually inside you. Move to better company: live with the Catos with Laelius, with Tubero.
~ Seneca (Letters From A Stoic. Letter CIV)
Think about all the things that we tell ourselves that we should stop doing, or start doing.
Those things that never end up stopping or starting, long term.
Could it be because of those we hang around with?
They are bringing to the surface, the same desire in us.
If you drink too much, stop hanging around those who drink.
If you swear too much, stop hanging around with those who swear.
Likewise, if you want to start exercising more, hang around with those who do.
If you want to start eating better, stop going to those places that encourage you not to.