Character Analysis
The Student
At first, the Self-Taught Man just seems like a quirky little dude who likes to hang around the Bouville library just as much as Antoine Roquentin does. But there is something about the little man's reading habits that doesn't sit right with Antoine, and one day, he figures it out.
In a flash of recognition, he remembers the names of the authors the STM has been reading and realizes that the guy is trying to read through every book in the library in alphabetical order:
Suddenly the names of the authors he last read come back to my mind: Lambert, Langlois, Larbalétrier, Lastex, Lavergne. It is a revelation; I have understood the Self-Taught Man's method; he teaches himself alphabetically. (9.2)
Now a lot of people would probably realize this and think the Self-Taught Man was some kind of weirdo. But Antoine admires the guy, as he writes:
I study him with a sort of admiration. What will-power he must have to carry through, slowly, obstinately, a plan on such a vast scale. (9.3)
It's important to remember that Antoine himself only spends time at the library in order to give his life some sense of purpose. He thus admires the Self-Taught Man's ability to distract himself from loneliness and depression by giving himself such a massive project to focus on.
There's a problem with the Self-Taught Man's project, though, just as Antoine realizes there is a problem with his own research project. Sooner or later, they'll be finished their projects and both Antoine and the STM will have nothing left to justify their lives. As Antoine writes:
[…] the day is approaching when closing the last book on the last shelf on the far left: [the STM] will say to himself, "Now what?" (9.3)
In other words, it's always nice to work toward a goal. But the sad part is that once you've reached that goal, you need to create a new one for yourself, then again, and again. Looking at life as an endless series of goals makes Antoine feel as though it's all pretty pointless in the end.
But that's not how the Self-Taught Man sees it. Instead of feeling like there's no point to life, he confronts despair by turning into…
The Humanist
Unlike Antoine, the Self-Taught Man doesn't actually go to the library out of despair. He does it because he likes to be around people in public places, even though he's shy. The STM, you see, is totally willing to admit to the fact that he needs to be around other people to survive emotionally.
This need dates all the way back to his experience as a prisoner of war during WWI, as he tells Antoine:
"[In] 1919, the year of my liberation, I spent many miserable months. I didn't know what to do with myself, I was wasting away. Whenever I saw men together I would insert myself into their group." (24.177)
On top of the fact that the STM loves all of humanity, he is also a political Socialist. This isn't really that surprising, since he believes that the point of human life is to increase the happiness of all humanity instead of individuals. But as he tells us, his decision to become a Socialist was preceded by some really bad feelings of despair:
"Before taking this decision [to become a Socialist] I felt myself in a solitude so frightful that I contemplated suicide." (24.187)
Like Antoine, the STM has gone through the experience of thinking there was no reason to be alive. But unlike Antoine, he has found a solution that satisfies him.
When Antoine tries to tell the STM that his humanism and Socialism are silly, the STM proves to be totally unshakable in his beliefs. Leaning across a restaurant table, he insists to Antoine,
"You love them at heart, Monsieur, you love them as I do." (24.277)
In other words, he simply won't believe it when Antoine claims not to love the human beings around him. After all, it sounds like all the STM has to keep him going is his love for humanity. So there would be no way for Antoine to take this away from him… without existentially killing him.
The Dark Secret
For much of this book, we can sympathize with the Self-Taught Man as a former prisoner of war who thought about suicide, then found hope through his love for humanity. It's a pretty inspiring story.
But Sartre throws a big ol' wrench into our affection for the STM when he decides to give this character pedophilic desires. Throughout the book, we know that the Self-Taught Man has been having problems with the librarian at the Bouville library. What we don't realize until the book's final chapters, though, is that the problem is sexual advances that the STM has been making on young boys.
This info takes us off-guard at first, as Antoine casually notes that the Self-Taught Man:
[…] was so little guilty: his humble, contemplative love for young boys is hardly sensuality—rather a form of humanity. But one day he had to find himself alone. (32.1)
In other words, Antoine sympathizes with the STM's love of young boys because he thinks it's a natural extension of his love for all humanity. But Antoine also admits that society would never accept this (y'think, Antoine?!) and that the STM will inevitably find himself an outcast.
When he first sees the STM make an advance on a boy in the library, Antoine can barely believes his eyes. And like most people, he feels disgusted when he sees the STM stroke the boy's hand, comparing the man's finger to a penis:
A brown hairy object […] hesitant. It was a thick finger, yellowed by tobacco; inside this hand it had all the grossness of the male sex organ. (32.23)
But when the librarian attacks the STM and gives him a bloody nose, Antoine jumps to the rescue and threatens to beat the librarian to a pulp. He tries to help the STM afterward, but the man is so ashamed that he walks away on his own. Antoine assumes that the guy is probably going to go off somewhere and commit suicide, then thinks otherwise because the STM is too gentle to commit violence. Even against himself.
The Self-Taught Man's Timeline