The root of the word "fatalism" is not so much "fatal" as it is "fate." While it is true that the same fatal fate awaits us all, fatalism is the belief that all events are predetermined by God, Providence, (The) Fate(s), etc. and that free will is nonexistent.
What is unclear, however, is why fatalism always seems to focus on fatality and not simply on fate. Isn't fate sometimes... good? Even within the framework of fatalism, if two teams compete, doesn't one win? Or is even that victory hollow, because it was going to happen no matter what, and those players were not so much "winners" as simply the ones it was necessary to win for the next series of events to take place? Further, if there is a God determining winners from losers, why do we assume that the losers will inevitably be us?
"Patterns" is a determinedly fatalistic song. And like the emo and Goth songs that followed, it focuses on the facts that some things "can scarcely be controlled," and that this is a bad thing. Fate has it in for us, and that's that. The overall imagery is that of darkness: "night," "shadows," "evening gloom," "dimly," "in darkness I must dwell."
Even the one mention of "light" is uncertain and menacing. This light "paints a pattern...like a[n] uneven scrawl." The light comes from one of Simon's most reliable images: a street lamp. In "Sounds of Silence," one had a halo. Later, in "Feelin' Groovy," the "lamppost" is friendly and has "flowers growin'." Here, the same light source is harsh and shows stark contrasts.
Two other sets of images come forth. One is that of an riddle, a "puzzle,", and a "maze." There is a path to be figured out, but the path is set, and there is but one way to change it: "The pattern never alters/ Until the rat dies."
Then there are images are of violence and constraint: "narrow," "impaled," "must," and "fell."
So we have a life of sightlessness, enigmas, and coercion. The system is entirely unfair, as the game is laid out for us, but we are not allowed to know the rules. We run the set maze blindly, only to be forced into a preset conclusion.
The result is a sense of powerlessness. The very leaves on the trees tremble with the fear of not-knowing. The speaker is unable to escape his room, left with nothing to do but desperately try to piece out "the puzzle that is [him]"... without even good light to work the puzzle by.
The speaker's Poe-like torment was triggered by a fractured shadow cast by the street lamp on his wall. But by the end of the song, the wall is the place not where the "light" struck, but "where darkness fell."
Musically, the song is interesting for two "world-music" elements. One is the sitar-like strings that open the song and form the bridge. The other is the galloping hand-drums of its rhythm.
The first imitates the "shivering," "uneven" elements in the song, the human uncertainty of how to proceed given the lack of information and the inevitability of the outcome.
The drums form the pattern itself-- driving, insistent, relentless (how different from the cheerful hand-drums of the later "Cecilia"!). In fact, the songs concludes with the strings strumming rhythmically, as if helplessly succumbing to the force of the drums' pattern, the way the "light" on the wall in the first verse becomes the "darkness" there in the last.
"Patterns" is fatalistic, but not necessarily nihilistic. There is one thread of hope, in the penultimate word: "scarcely." The speaker might well have said, in the same meter, "never." That which is "scarce" does still exist. The speaker still holds out the slim hope that some "control" over one's fate is possible.
("Patterns" can be thought of as forming a diptych with the song that follows, "Cloudy." They may seem polar opposites, but a closer look reveals that they are still opposite ends of the same pole.)
Next song: "Cloudy"