In his Sunday New York Times article "'Be Yourself' Is Terrible Advice," Professor Adam Grant of my alma mater, The University of Pennsylvania, states that, "Authenticity means erasing the gap between what you firmly believe inside and what you reveal to the outside world."
In fact, what Professor Grant provides is the exact definition of "congruence," not "authenticity."
Congruence is when what one reveals to the outer world matches his or her inner workings; authenticity, on the other hand, is usually denoted in contradistinction to our false selves, facades or personas - what we show the outer world. For instance, if you feel that your vocation is to be a great novelist or painter but you did not pursue that calling because your parents pressured you to go into business, then you would be inauthentic.
More importantly, these notions currently bandied about - such as "authenticity" as well as "mindfulness" and "compassion" - derive from the wave of Buddhist philosophy sweeping over the United States for the last fifty years. (Yes, of course, Heidegger spoke of authenticity, and compassion plays a large role in Christianity and Judaism, but I would argue that our contemporary understandings of these terms are heavily influenced by the presence of the Dalai Lama in our culture today. In particular, regarding compassion, I would bet that more Americans could identify His Holiness stating, "My religion is compassion," than find India on a map.)
Detached from the larger teachings, Westerners often attempt to apply psychological tests - such as the one Professor Grant mentions in his article regarding people salting their steaks - to prove scientific theories. But applying Western science to measure the efficacy of Buddhist principles is like trying to measure milk with a ruler. Devoid of a broader understanding of how the Buddha believed our minds function and why our minds have a negativity bias, the Buddha's prescription to alleviate suffering, which employs such concepts as authenticity, mindfulness, and compassion, represents another paradigm that Westerners are just beginning to appreciate.
The example of authenticity that Professor Grant cites in his article - namely author A.J. Jacobs deciding to speak his thoughts with no filter or "low monitoring" for a few weeks - has very little to do with authenticity. From the studies I have read, the average person has 50,000 to 90,000 thoughts everyday, the disproportionate number of them are redundant and negative. What Professor Grant claims to be authenticity would be better understood as mindful awareness of thoughts. If authenticity meant verbalizing the streams of consciousness that run through our heads - as is done in psychoanalysis - then every prison cell in America would be double-booked for the next 500 years. Which is why the Buddha devised the 8 limb path that incorporates such tenets as "Right speech," "Right mindfulness," and "Right actions."
Finally, in Buddhism there is no self to be. Hence the title "'Be Yourself' Is Terrible Advice" is correct, but it is correct for the wrong reason. And maybe it is equally unadvisable to quote a fictional fool here, but Polonius' advice to Laertes - "This above all: to thine own self be true" - could be updated for our epoch as Joseph Campell's "Follow your bliss" (cf. Elaine Scarry on beauty) or more colloquially as "Follow your guts," "Follow your intuition," "Follow your heart," "Have personal integrity," or "Be congruent..." rather than trying to be something that does not exist.
Maybe authenticity can only be defined negationally?