Either/Or by Søren Kierkegaard (1843)

Victor Eremita buys a secondhand writing desk, and when a drawer jams he loses patience and strikes it; a hidden compartment springs open, spilling two bundles of papers by men who never met. One set belongs to a young aesthete who lives for the exquisite passing moment, and holds a cold, dazzling diary of how a man engineers a girl named Cordelia into loving him and then into breaking their engagement herself, consuming the whole affair without ever once living inside it. The other belongs to a married judge who answers him in long, patient letters about duty, fidelity, and the strange courage of choosing your own life. Søren Kierkegaard gives each man his full strength and then, devastatingly, refuses to declare a winner. There is no third voice to settle the matter. The either/or of the title was never his to resolve; it is yours, and the book's deepest claim is that a life cannot be reasoned into, only chosen, again and again, until the choosing becomes who you are.