Let us never reckon that our work in fighting against sin — in crucifying, mortifying, and subduing it — is at an end. … We may think that we have thoroughly won the field, but there is still some reserve remaining that we did not see or know. Many conquerors have been ruined by carelessness after a victory, and many have been spiritually wounded after great successes. David’s great fall into sin followed a long profession, many experiences of God, and watchfulness in keeping himself from his iniquity. And this is part of the reason why the profession of many has declined in their old age or riper years. They have given up the work of mortifying sin before the work was finished. … It is as necessary to watch towards the end of the race as at the beginning. ‘Mortify therefore your members which are upon the earth’ (Col 3:5). ~ John Owen
To continue the analogy, just as a team can dominate the majority of a game and yet lose it because of sloppy play at the end, so too can we fall into sin because of carelessness, overconfidence, or spiritual laziness (among other things). Let us not fall into these traps, but cling firmly to Christ and continue to turn from the sin which so easily entangles us.
