A man’s love, till it has been chastened and fastened by the feeling of duty which marriage brings with it, is instigated mainly by the difficulty of pursuit.

Trollope contrasts romantic pursuit with the steadier moral commitments of marriage. The remark suggests that, before love is “chastened” by responsibility, a man’s ardor may be fueled less by genuine attachment than by the thrill of overcoming obstacles—competition, resistance, or social barriers. In this view, desire is intensified by difficulty, but that intensity is unstable: once the chase ends, the feeling may cool unless it is transformed into duty and constancy. The line reflects Trollope’s recurring interest in courtship as a social game shaped by pride, vanity, and convention, and in marriage as an institution that tests whether passion can mature into ethical commitment.