Stranger Than Fiction is a film about wrestling your own destiny from forces seemingly beyond your control. Harold Crick (Will Ferrell) is a bland taxman whose meticulous life comes unraveled when he starts hearing a voice narrating his actions.
At this point in the film, Harold has fallen for Ana (Maggie Gyllenhaal), a baker he was sent to audit. He has also recently started teaching himself the guitar, a lifelong dream. These threads reach their apex in this glorious scene. It's a great use of a simple song, first played quietly and unassumingly by our earnest hero, then cranked on the soundtrack as we get our sparkling screen kiss. It is another example of music being utilized as a dialect of the cinematic language.