I wish I could make the universe deliver wonderful things to my doorstep just by imagining them. I can't--and neither can you, no matter what anyone tells you. There is not a single piece of hard evidence that "visualizing success," and doing nothing else, will do a damn thing for you.
In fact, there is plenty of evidence  that it will leave you even worse off than when you started. Scientifically-speaking, focusing all of your thoughts on an ideal future reliably leads to lower achievement. In other words, you are less likely to achieve your goals when all you do is imagine that you already have achieved them.
"Negative" thinking, on the other hand, has gotten a bad rap. This is mostly because the people who advocate "positive" thinking lump all the "negative" thoughts together in one big unpleasant pile, not realizing that some kinds of negative thoughts are actually necessary and motivating. There is a big difference between "I am a loser and can't do this" (a bad, self-defeating negative thought), and "This won't be easy, and I'm going to have to work hard" (a very good negative thought that actually predicts greater success).
In fact, study after study shows that people who think not only about their dreams, but about the obstacles that lie in the way of realizing their dreams--who visualize the steps they will take to make success happen, rather than just the success itself--vastly outperform those who sit back and wait for the universe to reward them for all their positive thinking. Whether it's starting a relationship with your secret crush, landing a job, recovering from major surgery, or losing weight, research shows that if you don't keep it real you're going to be really screwed.
A new set of studies  by NYU psychologists Heather Barry Kappes and Gabriele Oettingen offers insight into why this kind of thinking isn't just useless, but actually sets you up for failure. These researchers found that people who imagined an uncertain and challenging future reported feeling significantly more energized, and accomplished much more, than those who idealized their future. The purely "positive" thinkers' lower energy levels even showed up in objective, physiological measurements. (Ironically, these studies showed that the more important it was to the participant that the dream come true, the more idealizing sapped their motivation!)
Kappes and Oettingen argue that when we focus solely on imagining the future of our dreams, our minds enjoy and indulge in those images as if they are real. They might be reachable, realistic dreams or impossible, unrealistic ones, but none of that matters because we don't bother to think about the odds of getting there or the hurdles that will have to be overcome. We're too busy enjoying the fantasy.
Admittedly, there are some people that might experience a benefit from visualizing a positive future or a vision board. People who are depressed, or have very low self-confidence, are more likely to think about obstacles, and only obstacles. They may need to be reminded that a positive future is possible, and a vision board when used hand-in-hand with some realistic thinking and planning, can be an effective tool.
Believe me when I tell you that I truly wish the Law of Attraction would work. I also happen to wish that Hogwarts was a real place, and that Antonio Banderas was my next-door neighbor. But wishing will not make it so, and that's exactly my point.
To learn more about proven strategies for reaching goals (ones that actually work), check out Heidi's new book Succeed: How We Can Reach Our Goals . Follow her on Twitter @hghalvorson . Her website is www.heidigranthalvorson.com .