Drink more water. Go to bed earlier. Go to bed earlier without my iPad. Meditate. Avoid sugar. Avoid self-diagnosing on WebMD. Eat some nuts occasionally. Learn Italian. These are just a few of my New Year’s resolutions. And by the time you read this, I’m sure some will have already been broken (not counting the ones that weren’t even made). But the thing is, I’m not alone. According to a British survey, a whopping 88 percent of us all fail to keep our New Year’s resolutions. What gives?

Willpower. In short, it’s defined as the ability to resist our impulses. It’s about doing what matters most, even when it’s difficult or when you don’t really want to. Willpower has been the subject of increasing research in the scientific community as we try to understand why some people have less willpower than others. As science begins to parse the neural systems, chemical messengers, and inner workings of the brain, we are discovering an ongoing battle — moments when willpower prevails, and moments when temptation gets the best of us. What’s more, researchers are discovering how to align the regions of our brains in order to help us make better choices.

Let’s be honest, as a species, we’re pretty bad at exhibiting willpower. It’s a primitive thing. Eating, having sex, and sleeping are vital for the survival of the species, so evolution has arranged for them to be hard to resist. And then there are activities like gambling, smoking, drinking, and taking drugs — pastimes that have no real survival value, but because they have tapped into our neurochemistry via the brain’s pleasure center, we chase them anyway.

It’s not easy living in a society with endless temptations. Do I even need to mention the snooze button? In-the-moment temptations spur short bursts of dopamine in the brain, making it difficult to focus on our long-term goals. Since this all takes place in the midbrain — a region primarily focused on short-term awareness — we are constantly forced to resolve between what we want to do and what we ought to do.

According to Kelly McGonigal, author of “The Willpower Instinct: How Self-Control Works, Why It Matters, and What You Can Do to Get More of It” and professor at Stanford University, “Our brains operate at three levels: ‘I will,’ ‘I won’t,’ and ‘I want.’ For many of us, the I-want part usually wins.”

Here’s why: When temptation and desire are on the rise, the nucleus accumbens — located within the midbrain and playing a central role in our reward circuitry — buzzes with activity. After all, the midbrain’s objective is to maximize pleasure and minimize stress, pain, and discomfort. It wasn’t designed with moderation in mind. However, a few brain fissures up from here is located the head honcho of the brain: the prefrontal cortex. It’s responsible for judgment, reasoning, and cracking the whip to keep our midbrain impulses from taking over.

When our willpower is tested, it’s a battle between those parts of the brain — the nucleus accumbens and the prefrontal cortex — with each competing for supremacy. Scientists have found that the prefrontal cortex, particularly the ventral medial and dorsolateral regions, show greater activity when a person chooses the option which appears to be better for the long run — like choosing the oatmeal versus the donut, or putting that Christmas bonus into savings instead of spending it. This region becomes active before we even make a decision, and exerts effort to control our impulses. Of course, we ideally want the judgment center of our brain to exercise good judgment and willpower, but a lot of things — alcohol, drugs, stress, lack of sleep — can hinder its success. And just like that, goodbye New Year’s resolutions.

Drugs and alcohol are particularly insidious when it comes to willpower. Not only do they activate the brain’s pleasure centers, but they also compromise the prefrontal cortex’s ability to consider the consequences. Similarly, sleep deprivation and stress have a huge impact on how efficiently our brain’s judgment functions. In high stress situations, the brain has less energy to exert willpower, and in turn, we act instinctively, making decisions with our midbrain and based on the short-term. In fact, stress easily triggers cravings and makes the pleasurable dopamine neurons even more excited by any temptation in sight.

Case in point: Warnings on cigarette packages can actually increase a smoker’s urge to light up. Yep. According to McGonigal, a study published in the Journal of Public Policy & Marketing found that warnings of death trigger stress and fear in smokers. Unfortunately, this anxiety then triggers smokers’ default stress-relief strategy: smoking. Is it logical?

Not even a little bit. But it makes sense based on what we know about stress. It also doesn’t help that the smoker is staring at a pack of tempting cigarettes as he reads the warning. So even as a smoker’s brain encodes the words “WARNING: Cigarettes cause cancer” and grapples with mortality, another part of his brain starts screaming, “Don’t worry, smoking a cigarette will make you feel better!”

Now here’s where it gets really interesting. Both behavioral scientists and neuroscientists have recently concluded that willpower functions in the same way as a muscle that gets exhausted by overuse. Trying to control your temper, ignore temptations, or battle an impulse all tap the same source of strength. These activities flex our executive function muscles in the brain and deplete our mental energy reserve, effectively causing “decision fatigue.” Let’s say you concentrated your energy to resist the desserts at the company potluck dinner. Your ability to resist temptation later in the day will now be weaker. You’re welcome.