Feeling lazy? Scientists call that a motivation deficit, and its one of the main symptoms of schizophrenia.

Now, doctors say they've uncovered the roots of schizophrenics' lethargy: "Inaccuracy in estimating how difficult an effortful goal would be." Confronted with a task, they seem to underestimate the pleasure they'd get out of it and overestimate the amount of effort required to accomplish it. If it sounds familiar, you're correct; everybody hits that wall. But it's a matter of degrees. In the study, which appears in the Journal of Abnormal Psychology, those diagnosed with schizophrenia were more likely than those without the disorder to misjudge effort.

So, for example, the study authors said in a news release that schizophrenics were just as likely as any of us to sit around eating potato chips and watching television. Low effort, high pleasure payoff. But people without schizophrenia could pull themselves away because they had a better grip on what kind of effort it would take to accomplish other goals.

"There's something breaking down in the process around assessing high-effort, high-reward goals," said David Gard, a psychologist at San Francisco State University, who led the study on a grant from the National Institute of Mental Health. "When the reward is high and the effort is high, that's when people with schizophrenia struggle to hold in mind and go after the thing that they want for themselves."

The study, touted as one of the first to "look at the daily activities of people with schizophrenia," was designed to be relatively open ended. With 47 schizophrenic participants and 41 without, they phoned them each four times randomly throughout the day and asked what they were doing. The researchers asked what they hoped to do later in the day and how they were feeling about it. This went on for seven days.

At the end of it, "independent raters" went through the results and coded the responses in rankings for high effort or low effort, or high pleasure or low pleasure. Whenever the schizophrenic participants had a complex-sounding goal, they were more likely not to reach it than those in the control group. "We knew that people with schizophrenia were not engaging in a lot of goal-directed behavior," Gard said. "We just didn't know why."

Now they know: same reason as anyone else who procrastinates on a project or skips a night out with friends. Fun as that night out may sound, you really don't want to shower, pick out something to wear and put make-up on, etcetera etcetera. For people with schizophrenia, that feeling is more debilitating.

But there's a trick to solving the problem. Break the effort into smaller, easier chunks. They give an exercise example: Don't tell somebody to lose weight, tell them to walk a little more each day. "That's something we would do for everyone else, but it might have been avoided in patients with schizophrenia because we thought they weren't experiencing as much pleasure from their activities as they actually are," Gard said. "We can help them to identify things that are pleasurable and reward them toward larger goals."

Source: Gard D, Sanchez A, et al. Do People With Schizophrenia Have Difficulty Anticipating Pleasure, Engaging in Effortful Behavior, or Both? Journal of Abnormal Psychology. 2014.