Misperceptions are at the root of many medication errors. For example, a nurse using the medication dispensing system to obtain hydralazine retrieves the wrong drug because a pharmacy technician had inadvertently filled the drawer with hydroxyzine instead. The nurse incorrectly perceives that the correct drug was retrieved because that was what the nurse expected to find in that drawer. Another example of an error based on perceptual factors is when hydralazine and hydroxyzine appear on the screen of the automated dispensing system in alphabetical sequence and, because the drug names are so similar, the nurse inadvertently selects the wrong drug.