If a man harbors any sort of fear, it percolates through all thinking, damages his personality and makes him a landlord to a ghost.

Douglas’s image treats fear not as a momentary emotion but as a contaminant that seeps (“percolates”) into every mental process. Once admitted, it distorts judgment, narrows perception, and gradually reshapes character—“damages his personality”—until the fearful person is no longer fully self-governing. The final metaphor, “a landlord to a ghost,” suggests that fear becomes an occupying presence: intangible, insubstantial, yet able to commandeer the inner life like an unwanted tenant. The line reflects a moral-psychological view common in early 20th-century self-help and religious writing, where courage is framed as a prerequisite for clear thinking and integrity.