According to Konstantin Stanislavski and Lee Strasberg, two founding fathers of method acting, the best performers possess the rare ability to channel deeply personal recollections and emotions through their characters.
These actors don't just play a role as written, they share every breath and straining sinew with their alter ego.
In Birdman, Michael Keaton inhabits the role of a middle-aged Hollywood star, whose glory days as a big screen superhero are long behind him.
It's the role of a lifetime for Keaton - the role of his lifetime, no less, nodding and winking to his two stints behind Batman's cowl under director Tim Burton in the late 1980s and early 1990s.
Art and real life playfully blur in Alejandro Gonzalez Inarritu's technically dazzling comedy, which was shot on location in New York.
In one of the film's bravura handheld sequences, Keaton strides purposefully through crowded, neon-lit Times Square in just his underpants as tourists clamour with their mobile devices.
Literally and figuratively, he bares his soul.
Inarritu and cinematographer Emmanuel Lubezki, who deservedly won an Oscar for sci-fi thriller Gravity, meticulously splice together each interlude to resemble a single, unbroken 119-minute shot.
If you look closely, you can see the joins but, as a feat of split-second timing, balletic choreography and directorial brio, Birdman is jaw-dropping - right down to the moment the camera casually pans to a drummer on the street playing the same beats and rolls of Antonio Sanchez's improvised jazz score.
Riggan Thomson (Keaton) rose to fame playing a superhero called Birdman in three blockbuster films.
Twenty years later, he masterminds a comeback with nervy producer Jake (Zach Galifianakis) by directing, writing and starring in a Broadway production of Raymond Carver's short story What We Talk About When We Talk About Love.
As opening night approaches and revered critics including Tabitha Dickinson (Lindsay Duncan) prepare to deliver their waspish verdict, petty squabbles between Riggan and his cast - popular Broadway star Mike Shiner (Edward Norton), leading lady Lesley (Naomi Watts) and current squeeze Laura (Andrea Riseborough) - threaten to derail the vanity project.
The leading man struggles to keep personal demons at bay, exacerbated by fractious exchanges with his spirited daughter Sam (Emma Stone).
Accompanied by a rambling voiceover from Riggan that reflects the character's mental unravelling, Birdman is a wickedly funny satire of a world of overinflated egos and barely concealed vices.
Performances are uniformly excellent, from Keaton's career-revitalising turn to Stone's fearless portrayal of a recovering drug addict and Norton's hilarious embodiment of an artist, who believes that, "popularity is just the slutty little cousin of prestige".
Peppered with affectionate verbal barbs aimed at Hollywood's current glitterati, Inarritu's picture is crammed to bursting with self-referential treats that demand a second and third viewing.
Birdman is the post-Christmas gift that keep on giving.