agreed. There's also evidence to back that up.

source: Get Anyone to Do Anything (David Lieberman, Ph.D. Psychology)

The second factor in making sure that you are understood has to do with expectation. Numerous studies show the powerful role that expectation plays in understanding and include such finding as (a) girls who were told they would perform poorly on a math test did so; (b) assembly line workers who were told that the job was complex was and difficult performed less efficiently at the same task than those who were told that is was easy and simple; and (c) adults who were given fairly complex mazes solved them faster when told that they were based on a grade-school level