The effects of stress on willpower are a staple of romantic comedies. A character goes through a difficult romantic breakup, and in the next scene, she is sitting on the couch smeared in ice cream with empty wrappers strewn on the couch. Because these breakdowns of willpower are so clear when they happen, you might think that stressful situations bring out your worst behavior.
If you're gung ho on quitting cold turkey, make sure you've got plenty of gas in the tank (and can keep filling it up). Common signs of an empty tank are summed up in the acronym HALT (Hungry Angry Lonely Tired). Also, if going cold turkey has failed you before, or if it sounds particularly painful, try other methods.