Conventional wisdom suggests that the "human factor" in critical care environments is reason for inadequate medication and patient safety. "Human factors" (or human factors engineering) is also a scientific discipline and practice of improving human performance. Using decades of human factors research, this paper evaluates a range of common beliefs about patient safety through a human factors lens. This evaluation demonstrates that human factors provides a framework for understanding safety failures in critical care settings, offers insights into how to improve medication and patient safety, and reminds us that the "human factor" in critical care units is what allows these time-pressured, information-intense, mentally challenging, interruption-laden, and life-or-death environments to function so safely so much of the time.