From Psychology Today:
The great surrealist artist Salvador Dali was described by his fellow students at the Madrid art academy as “morbidly” shy according to his biographer Ian Gibson. He had a great fear of blushing and his shame about being ashamed drove him into solitude. It was his uncle who gave him the sage advice to become an actor in his relations with the people around him. He instructed him to pretend he was an extrovert and to act like an extrovert with everyone including your closest companions. Dali did just that to disguise his mortification. Every day he went through the motions of being an extrovert and, eventually, he became celebrated as the most extroverted, fearless, uninhibited and gregarious personalities of his time. He became what he pretended to be.
Though the above article is light on citations, this phenomena of faking your attitude is actually physiologically sound. Researchers have found that grinning like an idiot or frowning like a sad clown actually produces happiness or sadness. The effect is so powerful that it can actually change your mood. If you’re sad or anxious or depressed, holding a fake smile for a few minutes can actually make you happy.
Psychology Today suggests the following:
Put a pen between your teeth in far enough so that it’s stretching the edges of your mouth back without feeling uncomfortable. This will force a smile. Hold it there for five minutes or so. You’ll find yourself inexplicably in a happy mood. Then try walking with long strides and looking straight ahead. You will amaze yourself at how fast your facial expressions can change your emotions.