GREED — and its crafty sibling, speculation — are the designated culprits for the financial crisis. But another, much admired, habit of mind should get its share of the blame: the delusional optimism of mainstream, all-American, positive thinking.

As promoted by Oprah Winfrey, scores of megachurch pastors and an endless flow of self-help best sellers, the idea is to firmly believe that you will get what you want, not only because it will make you feel better to do so, but because “visualizing” something — ardently and with concentration — actually makes it happen. You will be able to pay that adjustable-rate mortgage or, at the other end of the transaction, turn thousands of bad mortgages into giga-profits if only you believe that you can.

Positive thinking is endemic to American culture — from weight loss programs to cancer support groups — and in the last two decades it has put down deep roots in the corporate world as well. Everyone knows that you won’t get a job paying more than $15 an hour unless you’re a “positive person,” and no one becomes a chief executive by issuing warnings of possible disaster.

The tomes in airport bookstores’ business sections warn against “negativity” and advise the reader to be at all times upbeat, optimistic, brimming with confidence. It’s a message companies relentlessly reinforced — treating their white-collar employees to manic motivational speakers and revival-like motivational events, while sending the top guys off to exotic locales to get pumped by the likes of Tony Robbins and other success gurus. Those who failed to get with the program would be subjected to personal “coaching” or shown the door.

The once-sober finance industry was not immune. On their Web sites, motivational speakers proudly list companies like Lehman Brothers and Merrill Lynch among their clients. What’s more, for those at the very top of the corporate hierarchy, all this positive thinking must not have seemed delusional at all. With the rise in executive compensation, bosses could have almost anything they wanted, just by expressing the desire. No one was psychologically prepared for hard times when they hit, because, according to the tenets of positive thinking, even to think of trouble is to bring it on.

Americans did not start out as deluded optimists. The original ethos, at least of white Protestant settlers and their descendants, was a grim Calvinism that offered wealth only through hard work and savings, and even then made no promises at all. You might work hard and still fail; you certainly wouldn’t get anywhere by adjusting your attitude or dreamily “visualizing” success.

Calvinists thought “negatively,” as we would say today, carrying a weight of guilt and foreboding that sometimes broke their spirits. It was in response to this harsh attitude that positive thinking arose — among mystics, lay healers and transcendentalists — in the 19th century, with its crowd-pleasing message that God, or the universe, is really on your side, that you can actually have whatever you want, if the wanting is focused enough.

When it comes to how we think, “negative” is not the only alternative to “positive.” As the case histories of depressives show, consistent pessimism can be just as baseless and deluded as its opposite. The alternative to both is realism — seeing the risks, having the courage to bear bad news and being prepared for famine as well as plenty. We ought to give it a try.