Like all dreamers, I mistook disenchantment for truth.

The line contrasts the psychology of the “dreamer” with the posture of the disillusioned realist. Sartre suggests that losing illusions can feel like gaining truth, but that disenchantment is itself a mood or stance—one that can be as distorting as naïve hope. Read in an existentialist key, it warns against confusing emotional tonality (cynicism, bitterness, deflation) with lucidity: the world does not become more “true” merely because one’s expectations collapse. The remark also implies a self-critique: the speaker recognizes a temptation to treat negation—seeing through, debunking, refusing belief—as a privileged access to reality, when it may simply be another form of dreaming.