If you think, “It’s okay to buy the whole box of cookies. I’ll be able to stop at one,” remind yourself that, most likely, history shows that it’s incredibly difficult to stop at one and you’re likely to end up eating more than you had planned. Set yourself up for success by only buying a single serving, or throwing away all but one serving before you start eating. While you may be able to stop at one, why take the risk when you don’t have to?