Anyone who has ever been on a diet or tried to quit smoking knows how difficult it can be to attain a personal goal. One nibble of a chocolate chip cookie or puff of a cigarette can feel like failure, making it tempting to give up altogether. But research from Wharton marketing professor Marissa Sharif offers something better than an all-or-nothing strategy. She recently spoke with Knowledge at Wharton about how including cheat days — which she calls “emergency reserves” — can help people stay on track with their goals. Her findings also have implications for businesses that want to build stronger connections with their customers. Knowledge at Wharton: You have co-authored studies about the benefits of emergency reserves. Tell us about that and the context of your research. Marissa Sharif: On a very broad level, I imagine how to help consumers reach their goals, like trying to lose weight or trying to save money.…