It’s hard to pinpoint exactly when positive thinking became the star of the self-help industry. The idea of optimism is older than America itself (some accounts date it back to ancient Greece), and positive psychology has been validating its benefits since long before Oprah and Deepak Chopra.

Today, the power of optimism is trumpeted from the shelves of bookstores, the walls of yoga studios, and the podiums of leadership conferences. Countless studies in recent years have charted the benefits of optimism, including reduced risk of heart disease and stroke, better immunity, and improved job performance.

But if positive thinking is such a game-changer, why do people often have such a hard time quitting smoking, losing weight, finding a new job, or maintaining a regular gym routine? If positive thoughts somehow birth great outcomes, why do we often struggle to reach personal and professional goals? While being upbeat and optimistic clearly isn’t the worst thing we can do for ourselves, it seems like it’s not exactly spurring behavior change, either.

Dr. Gabriele Oettigen, a New York University psychology professor and researcher, has been studying the effects and realities of positive thinking for over 20 years. In her new book, Rethinking Positive Thinking, she points out that while optimism is a critical component of conceiving goals, it can also be crippling when it comes to actually working toward them. In fact, a cheery disposition and good attitude can zap the motivation needed to mobilize and strategize, leaving us with lofty ideas that never reach fruition. In other words, dreaming isn’t doing.

I spoke with Oettigen about what could be more a practical and effective approach: a concept she has christened “mental contrasting.” In her book, she argues that while optimism alone isn’t enough, positive thinking coupled with an understanding of the obstacles that stand in our way is the key to achieving significant behavior change.

Magdalena Puniewska: Your book centers on the idea that in order to successfully achieve our goals, we need to add a dash of realism to our positivity. Could you explain how that works?

Gabriele Oettigen: We all have goals, big and small, personal and professional. We may fantasize about what it would be like to achieve them—for example, how nice it would be to have that corner office or to be 10 pounds lighter. But after this bout of dreaming, what we should also do is perform a procedure called mental contrasting—that is, examine the barriers that stand in the way of us actually attaining that goal. Visualizing the desired future and then imagining the obstacles can actually help us be more successful than positive thinking alone.

Puniewska: You argue that being optimistic about the future is not enough. Why not? Why can’t a positive attitude carry you on to achieving your goals?

Oettigen: The problem that we often run into with this is that when people only think about a positive future, they’ve already attained this future in their minds, so they have little motivation to actually act on it. We saw this in many of our studies: When we had participants just dream about a positive future, whether it was losing weight or asking a crush out on a date, those that simply fantasized about it were less likely to shed the extra pounds or find the courage to ask out a potential love interest, because in their mind, they had already done so. They imagined themselves, for example, as being slimmer, so they had no incentive to take action. They were already slimmer in their head. When we followed up with them weeks or months later, we found that they were less likely to have taken action than those participants that had indulged in a positive reality, but then were also asked to perform mental contrasting.

Puniewska: So, are there any instances where dreaming can be a good thing?

Oettigen: Dreaming can provide a welcome distraction if you’re faced with a waiting game in which you have no control, like waiting for test results or exam scores. It’s when there isn’t even the option of taking action that fantasies can be beneficial, because they allow for an escape.

It also depends on how you define dreaming. If you say that fantasizing about the future can give you information about what you really like and don’t like, then dreams are a great sort of virtual exploration, where you can investigate your desires without a commitment. For example, let’s say you are a college student and you’re thinking about what professional routes to take after you graduate. You may sit down and think about becoming a nurse and how nice it would be to interact with patients and take care of them. Plus, you really like biology class. But then as you’re fantasizing about your day at the hospital, you think, well, the hours would be really long, and a lot of nurses suffer from burnout—what you really want is more of a 9-to-5 job, still in the medical field, but just not as demanding in terms of hours. Your wish will change from “being a nurse” to “finding a job in the medical field that still allows me ample leisure time.” By doing this kind of dreaming, you can really dig deeper and explore your interests and needs.

Puniewska: In that case, you’re not necessarily thinking about the obstacles just yet. It’s kind of like a pre-process to determine what your wish really is?

Oettigen: Correct, and very often we want to achieve so many things at once, we can’t even prioritize which one we are willing or even able to tackle. The idea of mental contrasting is that it can help you select projects that are feasible and let go of projects that are lingering.

Puniewska: Consciously labeling your hurdles seems like such a critical step in goal-attainment. Why do people choose to circumvent it?

Oettigen: Well, it’s not something that’s inherently pleasurable. When you are thinking about obstacles, you need to have a little bit of courage to actually look at what about yourself is keeping you from achieving a goal, and that can sting a little bit. Being introspective is certainly engaging, but sometimes you will find out new things about yourself that can be a little daunting at first. The current literature has also pushed us to embrace this idea of positive thinking so much that we shun anything negative, and obstacles by nature are a negative thing. So, we tend not to consider negative concepts or ideas and instead focus only on the positive, which our research shows isn’t actually very helpful at all.

Puniewska: Once you do establish your obstacles, what should you do next?

Oettigen: Identifying obstacles is important, but it is also key not to dwell on them. You want to integrate the obstacles into images of the desired future and then develop a plan that will help you circumvent or address the anticipated hurdles. That way, you know how to respond to a situation. In the 1990s, Peter Gollwitzer was conducting research on a planning process—he called them implementation intentions, or “if-then” behavior plans. These plans specify how to act if a certain situation occurs. He was finding that people who had formed such plans were much more likely to attain their goals.

My colleagues and I found that mental contrasting led to wish fulfillment and behavior change because it produces an unconscious association in your brain between the future and the obstacle, and between the obstacle and the behavior to overcome it. Mental contrasting forms such associations, and people become more energized and more committed to the goal. Since commitment to the goal is a prerequisite for implementation intentions to work, we decided to combine mental contrasting and implementation intentions in a procedure named WOOP: wish, outcome, obstacle, plan. In a study on bad snacking habits, we found, for example, that participants who used WOOP reported more progress in breaking their bad habit—they were more likely to report that they didn’t eat junk food or dessert—than those who were told only to use mental contrasting and those who only used implementation intentions. To this effect, you want to adopt such a chronology of behavior: Find your wish, imagine the best possible outcome for this wish, pinpoint the most critical obstacle in the way and imagine it happening, and then establish a plan of how to overcome this obstacle.

Puniewska: Developing a measure to examine fantasies and dreams seems like a daunting task, because they’re not really tangible concepts. How did you come up with a way to do this?

Oettigen: I found that letting people explore their wishes and desires through imagining their fulfillment and writing these thoughts and images down was the best way. Because these are free thoughts and images continuously emerging in the stream of consciousness, there isn’t a way to really capture them by using traditional self-reporting questionnaires.

Puniewska: You also studied how our energy to complete a goal can be measured with physical things like blood pressure. How did your research examine the biological mechanisms at work?

Oettigen: Blood pressure is a very rudimentary indicator of energy and motivation. As we prepare to achieve a goal, our bodies take in more oxygen and nutrients, pumping in more blood to help equip us for whatever is ahead. This process hikes up energy and produces a slight increase in blood pressure. In studies where we tracked blood pressure, we found that simply having positive fantasies about the future actually lowered systolic blood pressure. Participants became too relaxed and it showed up on their physiological tests. This is exactly what you don’t want to happen as you’re planning to tackle a goal. You want to be empowered; you want to be motivated. If you feel too much at ease, you’re less likely to take action.