In the first sentence of paragraph 14, the author uses parentheses primarily to add an ironic qualifier to a broad statement.
The sentence reads: "In human affairs, it is almost never the case that one person, acting alone, can completely defeat themselves (although it is not for lack of trying)."
The parenthetical phrase "(although it is not for lack of trying)" adds a touch of irony to the broad statement that one person cannot completely defeat themselves. The author is suggesting that, although it is difficult for a person to completely defeat themselves, humans often engage in self-defeating behavior, despite their efforts to the contrary.
Therefore, the correct answer is E. add an ironic qualifier to a broad statement.