You thought you hated the girl who was a swot in school, yet now realise you envied her self-discipline and willpower.
The same applies to the skinny bitch in work who never succumbs to chocolate, the friend who leaves a party at midnight and avoids a hangover, and the mum-of-five whose children do French, ballet and yoga, while you drag your two kicking and screaming to swimming.
Kelly McGonigal is a health psychologist based at Stanford University in California, and unconventionally teaches yoga and meditation as part of her college psychology course.
She writes on mind and body issues for many publications, including the New York Times and the Washington Post, and believes willpower can be strengthened like a muscle -- and plays a vital role in our success in life.
"Willpower is about finding the energy and courage to do what really matters to you, even when it's difficult, and even when a part of you is afraid or unwilling," she says.
Her new book, Maximum Willpower, explains how we can successfully break bad habits, like not being able to pass the fridge without eating something. It tackles how we can conquer procrastination and manage stress and negative emotions.
It also focuses on how and why we give into temptation such as having another glass of wine, and how we can find the strength to resist the second half of the bottle.
According to McGonigal: "The book will explore the latest research on self-control and motivation, explain why guilt, stress, and self-hate only get in the way of willpower, and offers practical strategies rooted in science, mindfulness, and self-compassion."
The college professor also believes willpower -- the ability to control our attention, emotions, appetites and behaviour -- has far-reaching consequences for our day-to-day experiences, including whether or not we are happy or depressed.
In fact, scientific studies through the years have linked high levels of self-control to better health, relationships, and finances. Small things such as breaking habits, even if it's just brushing your teeth with the opposite hand, can increase our levels of self-control.
McGonigal also believes willpower is a mind-body response, and not a virtue. She feels it is a biological function which can be improved through mindfulness, exercise, nutrition, and sleep.
It is not an unlimited resource either and, believe it or not, too much self-control can actually be bad for your health, leaving you feeling tense and overly rigid.
Temptation and stress hijack our brain's systems of self-control, yet our brain can be trained for greater willpower, and be made ready to resist bad habits while we are under pressure.
Guilt and shame over our setbacks can also lead to us giving in again, yet self-forgiveness and self-compassion will, in fact, boost self-control instead of making us weaker in the long run, McGonigal believes. In fact, giving up control is sometimes the only way to gain self-control.
Willpower failures are contagious too -- you can catch the desire to overspend or overeat from your friends -- but you can also catch self-control from the right role models.
Here are some of McGonigal's tips for boosting willpower -- by breaking old habits, raising self-awareness, challenging ourselves and exercising.
1get at least six hours of sleep a night Just one night of sleep deprivation (less than five or six hours of sleep), can result in mild dysfunction in the prefrontal cortex, research suggests. "We turn into the worst version of ourselves,'' says McGonigal, "and are more likely to snap at our kids, lose our concentration when driving, and pig out on junk food."
2practise slow- breathing techniques Those who engage in formal meditation for 15 minutes a day actually add grey matter to their brain's prefrontal cortex, according to a recent study from Massachusetts General Hospital. Other studies have found that meditators exhibit higher levels of self-control.
In McGonigal's book, she includes this instant willpower booster to try: "Slow your breathing down to four to six breaths per minute. That's 10 to 15 seconds per breath.''
3do something challenging Adopt a new habit, such as brushing your teeth with the opposite hand or adjusting your posture every 30 minutes, both of which have been shown to increase willpower in research.
Or take up a new skill or hobby such as rollerblading, Zumba, or ballroom dancing.
4exercise every day, preferably outdoors The biggest mood-boosting, stress-relieving effects of exercise came from five-minute doses, according to a 2010 review of 10 studies.
Getting active outside provided an added bonus of increased willpower in some studies, possibly because being around nature reduced stress more than being indoors.
5make sure your body is well fuelled Hunger definitely depletes self-control, so eating regular healthy meals is key to staying strong.
If you're gearing up for an intense project -- or are in the middle of one -- having a small carbohydrate snack such as an apple or a handful of breadsticks can provide the brain with much-needed glucose to see you through.
Maximum Willpower: How to Master the New Science of Self-control, by Kelly McGonigal (Macmillan, €15.85) will soon be available from book shops