There's a certain suspension of disbelief required for all cinema, an acceptance that what we're seeing on screen is "reality" rather than a bunch of actors, lighting specialists, sound techs, set builders, cinematographers and a director all collaborating to tell a compelling story. With some genres of film, there's a second level of belief required, one where the viewer has to also accept the basic premise of the film.
That's where The Mechanic fails miserably, presenting Arthur Bishop (Jason Statham) as a crack assassin who can kill his targets without leaving a trace, or even - as we learn later - to implicate third parties in the crime. Impressive. Except as we watch Bishop blunder his way through target after target, he's clearly amateurish, leaving fingerprints and clues at every crime scene, never having a backup plan if something goes wrong and relying on luck to escape afterwards.
There's an predictable father/son relationship between Bishop and his "handler" Harry (Donald Sutherland) which is reinforced by Harry complaining to Bishop about his ne'er-do-well son Steve (Ben Foster). In one particularly odd scene, Bishop offers parenting advice to Harry, even though he prides himself on being disconnected from his own emotions. Through an obvious plot machination, Bishop ends up an unwilling mentor to Steve, a dangerous thug with no sense of elegance or finesse.
Ultimately, the glue that makes The Mechanic stick together is action film cliches. From the opening scene where we see a drug lord getting off his private jet in Columbia, it's hoary action cliches that fuel the story. Problem is, it's ultimately boring and even Statham's usually entertaining fight sequences are muted and incomprehensibly filmed, leaving us to pay too much attention to the weak plot. This just isn't a good film.