Same with food. If I have unhealthy food in the house, I will eventually eat it in a moment of weakness when I experience a dip in fortitude. So the solution has been to not allow bad food in the house, by never shopping on an empty stomach. And ensure I always have a whole lamb in the freezer.

Another trick is to go shopping on my bicycle, so I can only buy what fits in a backpack - and usually that's high-nutrition items.