This is the basic premise of the movie: a happy, 30-year-old British woman who hasn't got a care in the world (or doesn't appear to) and lives life from day to day laughing at everything. She takes driving lessons from a rather harsh instructor (Eddie Marsan), and yet throughout his tantrums, she continues on joking and looking at the brighter side of things.
Yet as one can guess with a story like this the character arc will inevitably lead to Poppy confronting something really serious that will break down her cheerful demeanor. Such events are necessary to make Poppy feel like a real character, and its a great credit to Hawkins and Leigh that when this scene comes, it actually does feel genuine and gets an emotional response from the audience.
The movie is about being happy, though, no matter what happens in your life. Poppy demonstrates that you can't brush everything away, but you can pick yourself back up and carry on, learning what you have learned. This movie is like Amelie (2001) because it just wants you to be happy when you watch it (Amelie did lack any dramatic scenes, but that's beside the point). As Poppy's friend Zoe (Alexis Zegerman) says, "You can't make everyone happy." "While there's no harm in trying, is there?" chirps back Poppy.