Perhaps you’ve had the experience of reaching the end of a day on which you’d been unusually successful in getting your work done, or sticking to your fitness routine, but then instead of thinking “What a great day!”, you think: “That’s the kind of day I’m aiming for, and now it’s my job to make sure I keep on having more and more of them!” The result: you turned a potential source of easy delight into a source of further stress.