In general you're better off reading the book when the film is just an adaptation, as the book can give more context, inner dialogue etc than a film can, simply due to the medium.
There are of course exceptions. Famously, Palahniuk has said the Fight Club film captured his intent better than his novel did. I also think film of The English Patient, which covers only a tiny section of what I consider a forgettable novel, is quite good, but even if you disagree I think almost anyone would say the film is better. And of course plenty of films aren't novel adaptations.
Regardless, if you're looking for a "story that could change my life" you're likely to get much more from the text than the adaptation. The strengths and weaknesses of the two media are just too different.
My limited understanding is that Palahniuk's book was a kind of fuck you to the publishing establishment (and in that vein, I highly recommend American Fiction).
Fight Club is one of my favorite movies of all time (although I could do with less onscreen fighting). It was (to me) part of a cosmic trilogy of movies ending the millennium:
* Fight Club
* American Beauty
* The Matrix
All three dealt with the concept of sleepwalking through life and the shock of waking up from it.
There are of course exceptions. Famously, Palahniuk has said the Fight Club film captured his intent better than his novel did. I also think film of The English Patient, which covers only a tiny section of what I consider a forgettable novel, is quite good, but even if you disagree I think almost anyone would say the film is better. And of course plenty of films aren't novel adaptations.
Regardless, if you're looking for a "story that could change my life" you're likely to get much more from the text than the adaptation. The strengths and weaknesses of the two media are just too different.