The first weeks of a new year can be tumultuous and invigorating. It’s the moment we consider the unstoppable passage of time—how did it get so late?—while trying, more intently than usual, to map out our as yet unwritten future.

Following that map, of course, is the hard part. As reliably as the calendar changes, resolutions fall by the wayside, and old habits reassert themselves. We know it’s going to happen, and we think we even know why. After a while, the necessary willpower to delay gratification in the interest of an abstract future benefit gives way to temptation. It seems straightforward enough: We fail because now is more powerful than later.