In Greek and Roman Mythology, Narcissus stared at his own reflection, so absorbed in his own image he was oblivious to anybody else. The idealized image that he saw withdrew him from the world. He was in an emotional vacuum, devoid of anything but what he wanted to see.
But aside from Narcissus, and those suffering from the psychological condition of narcissism, our own self-reflection can provide us the kind of useful assessment that allows us to live up to our own standards.
Researchers Robert Wicklund and Shelley Duval discovered back in the 1970s that when people were in front of a mirror and told they were being filmed, those people changed their behavior in very positive ways. They worked harder, gave more accurate answers to questions, were more consistent in their actions, and acted more consistently with their values.
About a decade later, Charles Carver and Michael Scheier looked at this in more depth, and within their larger explorations of self-awareness and self-regulation, found something fascinating.