Ralph Erskine (Self-conceit dissected), Sermons 1:364-365:
What! am I a dog, to do so and so! Men persuade themselves, through self-conceit, that their nature is not so far venomed, that it should break forth into such wickedness. Indeed, there may be some sins that we are not so much tempted to as others: so Luther said of himself, “That he never was tempted to covetousness.” Yet there is no sin but we may both be tempted to, and, through temptation, even fall into, if the everlasting arms do not under-prop. This is supposed in that motive adduced, Gal. 6:1, “Brethren, if any man be overtaken in a fault, ye which are spiritual, restore such an one in the spirit of meekness; considering thyself, lest thou also be tempted.” We need to suspect our own hearts, if we knew our nature: however they may be tamed by education, civility, good example, and the like. As you would readily suspect a bear, or wolf, or lion, or any such like beast, and be loath to trust yourself to it, though never so well tamed, knowing its natural voracious disposition: even so, “He that trusteth in his own heart is a fool,” and he that leaneth to his own understanding is not wise. Fear even those sins which ye least suspect, and to which you find not yourselves so pronely carried.