The human brain is fickle when it comes to commitments. Between 60 and 80 percent of people don’t use their gym memberships. Most diets work at first but backfire in the long run. According to a 2007 survey conducted by the British psychologist Richard Wiseman, about 88 percent of New Year’s resolutions end in failure.

Given how widespread our broken pledges are, it’s no surprise that psychologists study human willpower. Florida State University Professor of Psychology Roy Baumeister is one of the main figures in this area of study. His research on willpower began in the late 1990s with a few papers demonstrating that when people exert willpower, self-control, persistence and rationality founder. Willpower, he discovered, was a limited resource easily drained by everyday activity.

This article summarises three studies on willpower.

#1:

[H]uman willpower is exhaustible. Under this paradigm, exercising willpower in one instance reduces our ability to decide optimally, exert self-control or perform well on tasks in proceeding instances. Willpower is like a muscle, when it’s depleted – what Baumeister termed “ego depletion” – we suffer the consequences.

#2:

This might not be the whole picture, however. A brand new paper by Michael Inzlicht (University of Toronto) and Brandon J. Schmeichel (Texas A&M University) propose that, “[ego depletion] is not some mysterious result of lost self-control resources but rather the result of shifts in motivation, attention, and emotion.”

#3:

There are other reasons to believe that ego-depletion might not be about “resource depletion.” A few studies provide evidence that participants who work hard on an initial task feel justified in slacking off during subsequent tasks. Research from Veronika Job, Carol Dweck and Gregory Walton even found that participants who believed that willpower is unlimited showed fewer signs of ego depletion compared to participants who thought willpower is limited, suggesting that reduced self-control is a function of people’s folk psychological beliefs. Taken together, our struggles with willpower might be a struggle with motivation and perception.

The article’s conclusion:

Motivation and attention are, of course, interdependent, “[The] shift in motivation away from restraint and towards gratification is accompanied by a parallel shift in attention away from cues signaling the need to control and towards cues signaling the possibility of reward.” However, it is unclear which way the casual arrows points.

What is apparent is that a decade worth of research on willpower is incomplete. Inzlicht and Schmeichel aren’t in the business of destroying paradigms. They emphasize that previous research by Baumeister and colleagues is valuable and state that they’ve contributed to it. But they advise psychologists to understand self-control and its depletion at a more mechanical level. “That self-control exertion at Time 1 affects self-control at Time 2 has been replicated over 100 separate times,” they affirm. “Now we need to gain a more precise understanding of why that is.”