Got a monster to-do list? Don’t overthink it.

May 31, 2012, 1:53 PM UTC

FORTUNE — Everybody knows that the best way to accomplish a long, complicated list of goals is to plan each step of every task — right? But if you’ve taken that approach and found that, the more detailed your plans, the less you actually got done, cheer up: It seems that’s normal.

“Despite good intentions, most goals go unfulfilled,” says Amy Dalton, who teaches marketing at the Hong Kong University of Science and Technology. She and Stephen Spiller, an assistant professor of marketing at the Anderson School of Management at UCLA, teamed up on a series of studies to find out why that is.

The full research results will be published in a study called “Too Much of a Good Thing: The Benefits of Implementation Intentions Depend on the Number of Goals,”set to appear in the October issue of the Journal of Consumer Research.

Turns out, detailed planning works quite well if you have just one big item on your to-do list. The longer your list, however, the less useful it is to make your plans too specific.

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“If you have six things to do today, all high priority, and you sit down and start planning everything out in detail, you quickly realize how difficult it will be to do it all,” Dalton explains. “You feel overwhelmed and, because you don’t think you can pull it all off, you’re less committed. By contrast, people who don’t form specific plans are more likely to believe they can achieve it all.”

Here Henry Ford’s famous dictum kicks in. “If you think you can’t, you’re right,” he said. “If you think you can, you’re right.” To avoid paralysis by analysis, Dalton suggests, “save the detailed planning only for your most important goal.” For everything else, as a certain sneaker company’s slogan says, just do it.

One odd twist: Dalton and Spiller found that many of us can avoid tripping over our own plans even with multiple goals — as long as we are led to believe that peers have even more on their plates. “People who think that others have more to do than they do are less overwhelmed by their plans,” Dalton says. Why that should be so is not clear, but it may simply be human nature to try to keep up with Joneses — or with the guy in the next cubicle.

Are people in some jobs more likely to finish their to-do lists than others? A recent LinkedIn survey of 6,500 professionals around the world suggests so. Poll respondents in the agriculture industry ranked highest: 83% said they usually get their entire daily to-do list done. Attorneys scored lowest, at 66%. Everybody else in the survey fell somewhere in between. An encouraging thought: No occupational group claimed a 100% score.