If he thought about it, he'd go insane.
If he were to literally think about the situation he was in, “trapped” in an elevator all day, transporting his former classmates up and down the levels of the building, he would go insane. Especially knowing that he was capable of achieving things far greater than being an elevator man. Instead of thinking of the literal reality of the situation, he tries to face the circumstances almost “figuratively” in a sense.
To help improve the meaning of these lyrics, visit "Elevator Man, 1949" by Rita Dove and leave a comment on the lyrics box