Breaking the Fourth Wall; Flashback
In keeping with his "Maximum effort!" catchphrase, Deadpool employs a pair of splashy narrative techniques to tell the titular character's tale.
Breaking the Fourth Wall
Deadpool regularly breaks the fourth wall to address the audience directly. It's a technique that meshes well with his self-awareness and inability to stay silent for more than ten consecutive seconds. Like Bugs Bunny, Ferris Bueller, and Patrick Bateman before him, Deadpool uses direct address to make jokes and to explain himself and his movie:
DEADPOOL: You're probably thinking, "My boyfriend said this was a superhero movie, but that guy in the red suit just turned that other guy into a f***ing kebab!" Well, I may be super, but I am no hero. And yeah, technically this is a murder, but some of the best love stories start with a murder. And that's exactly what this is: a love story.
Your English teacher probably told you that good writers "show, don't tell." Clearly, Deadpool's never met your English teacher. As the example above demonstrates, he not only wants to make us laugh, but he also wants us to know what makes him tick and how to understand his origin story. Control freak much?
Deadpool is an origin story that's told mostly through flashback. During the film's opening credits, Deadpool's already knee-deep in the film's first big fight scene: a highway clash between Ajax's convoy and our masked protagonist. From there, we flash back to Deadpool's cab ride to that fight. Then we flash back two years before that, to where our story really begins, with Wade Wilson the mercenary, intimidating a sketchy pizza delivery guy for tequila money.
The effect of all this flashing back in time emphasizes Wade's transformation into Deadpool, as well as his motivation for said transformation. By that we mean that, when we first meet Deadpool, it's quickly apparent that he's not like other superheroes, and that makes us want to know where in the world this trash-talking, hyper-violent dude came from.
Once our curiosity is peaked, the film helpfully flashes back to a kinder, gentler Wade. He meets Vanessa and falls in love, and then we really wonder how he ended up in a full-body costume skewering bad guys like teriyaki chicken on the expressway. The flashback explains it all. It also underscores that, beneath the clever quips, Deadpool's just a guy who misses his girlfriend.