No, Memento is not a post-modern existential film with the purpose of making us believe that everyone harbors their own truth. Rather, it takes the audience through a world were memories cannot be trusted and facts will be lost in minutes if they are not recorded in in on photographs or on the body. The editing style forces the audience into the mind and experience of Leonard, who suffers a rare condition of short term memory loss after his "incident." The cuts and breaks make the audience scramble to remember what has happened (just like Leonard) and force the reader to question time in hopes of discovering the truth.
The movie works through two alternating story lines. Both follow Leonard but they seem to be at different times. They are marked by black and white versus color. The black and white scenes move more or less chronologically. The color scenes move forward (except for the very first scene which actually moves backward) but they move backward in segments. For instance, in each scene (again, except for the first one) the action happens forward but plays out up until the beginning of the last scene. With each new color scene we are witnessing what happened just before the last color scene started. With both of the story lines happening (with the same character apparently dealing with the same problem) by jumping back and forth, the audience really has to focus on what is going on in each one. Each time the screen cuts back to the other story, the audience has to remember what is important here and how it all fits together. In addition, the color scenes force the viewer to remember what was just happening before. This makes the audience feel as though they have short term memory loss just like Leonard.
With all the cutting scenes back and forth, the audience has to pay attention to the characters as well as the story line. Further, as the movie works its way backwards the audience has to struggle to piece together the characters and their relationships before any of it is explained. Leonard notes that sometimes he feels strange or feels as though someone is trying to get him to kill the wrong man but he cannot place the feeling or remember why. The same is true of the audience--we can work hard to understand the characters but through the whole movie it is easy to get gut feelings about the characters while we anxiously anticipate the truth about them. When Teddy tells Lenny that "you don't know who you are," the audience realizes that we do not even know the one character we had depended on knowing. In one scene, the character is describing the condition that Sammie faced. The camera cuts to him sitting in a mental hospital but as the doctor walks by there is a quick flash of Leonard sitting in the chair instead. This is one of the moments where the editing gives the viewer a gut feeling but one that is unexplainable.
The movie does not just feature short term memory loss, but comments on time through the disjointed editing style. At one point in the film, Teddy tells Lenny, "you don't even know how long ago [the incident] was." This draws the audience's attention suddenly to the fact that we have no indication for how long it has been since his wife's death. At another point in the movie Leonard is burning his wife's things and he realizes that he has probably done this a million times before--he "can't remember to forget." The feeling that this is all happening in an unknowable amount of time is not kept from the audience but pressed on them. As we jump from shot to shot or scene to scene there is know way for the audience to determine how much time has passed.
At the very end of the film (which is really the beginning of the story) the characters have all given their ideas of what is happening. The only problem is that by that point in the film, the audience is seeking to remember every detail to see if the stories check out. However, after all the disorienting cuts and transitions, it is almost impossible to check the stories (especially Teddy's) against the "truth" we saw in the movie. Further, we are even more skeptical of each characters level of integrity and truthfulness. This is when the audience knows that they are truly in the position of Leonard. Earlier he had noted that memories are fallible and untrustworthy. What matters are the facts. However, we can only go on memories to determine which character is right about what happened. We must depend on Leonard, Teddy, Natalie, and our own memories (which in a movie as confusing and complex as this, is very difficult) for the evidence in determining the truth.
The consistently abrupt shots, unknowable time frames, and disorienting sequence of events leaves the audience feeling the effects of short term memory loss. In one of the most shocking moments of the film, Leonard is telling Natalie that the last thing he remembers is his wife. The scene abruptly cuts to an extreme close-up of his wife's eye blinking beneath the plastic over her face. Then, the scene cuts back to the bar and Leonard continues, "dying." The cuts and unconventional sequence of events leaves the audience disoriented and off balance, constantly trying to remember and working desperately to understand the truth.