Georgette Heyer said this quote

The Reverend William Trent, whose mind was of a serious order, had several times warned his elder sister that too lively a sense of humour frequently led to laxity of principle. She now perceived how right he was; and wondered, in dismay, whether it was because he invariably made her laugh that instead of regarding the Nonesuch with revulsion she was obliged to struggle against the impulse to cast every scruple to the winds, and to give her life into his keeping.