…had the heart been well guarded at first, it had never come to this height: the temptation had been stopped in the first or second act. And indeed there it is stopped easily: for it is the motions of a tempted soul to sin, as in the motion of a stone falling from the brow of a hill; it is easily stopped at first, but when it is set agoing, [it gathers strength as it goes]: And therefore, it is the greatest wisdom in the world to observe the first motions of the heart, to check and stop sin there. The motions of sin are weakest at first, a little care and watchfulness may prevent much mischief now, which the careless heart not heeding, is brought with the power of temptation. (John Flavel, from A Saint Indeed, emphasis mine)
