"Downfall" is not an adjective, nor is it a noun for a type of person. Definition of downfall
You can say that a person has "fallen down" of course, when they fall on the floor, or fall down the stairs.
You can say that someone is "downtrodden", meaning that someone else has treated them as an inferior, sometimes leading to the downtrodden person actually feeling inferior. A very domineering husband might have a downtrodden wife.
I own the book. There is no comma after downfall; the word is part of the phrase which continues on the next line. The whole phrase reads downfall could be desire for material goods. It means 'your quest for material goods could be your downfall".
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