127 Hours is how long hiker Aron Ralston spent trapped in a Utah canyon in 2003 before he cut off his arm to get free and hike to safety. It’s a true story, adapted for film by Danny Boyle (best known for Slumdog Millionaire) and starring James Franco as Ralston.

This film—indeed, any film—is only as good as its source material, and that’s where the limitations of 127 Hours become apparent. If you’re going to stick to the true story, then there’s only so much you can do with the plot: Guy goes hiking, gets his hand stuck, cuts it off, and lives to tell the tale. You can toss in some hallucinations to vary the scenes a bit, but ultimately the story is what it is.

We can’t fault the screenwriters (director Boyle and Simon Beaufoy) for that, nor, I suppose, even Ralston, who fleshed out his experience into a 354-page book. The scenes of him hiking in the desert before his accident are not terribly interesting, and nor are the scenes after he frees himself. This leaves the middle third as the meat of the film, after he’s got his hand stuck and after he steels himself enough to hack it off.

Ralston spends the time trying to make the best of his situation, trying to survive, and hallucinating. Ralston survived partly due to his wits and bravery, but Ralston is no hero; he’s an arrogant idiot who not only hiked alone but didn’t bother to tell anyone where he was going, thus preventing a search. Sure, cutting off your own arm takes more balls than most people have, but it’s also not as if he had much of a choice: It was do-or-die, and Ralston decided to do. It was the only decision he could make after having made a series of bad decisions.

Three Stars

Stars: James Franco and Amber Tamblyn

Director: Danny Boyle

Plugs: Coca-Cola products