Much the same can be said about human action. Aquinas said the way to do good was to work at it. The virtue of prudence is what helps one do good and avoid evil. However, in a life that has not been properly weeded, this becomes difficult. It's amazing how sin can beget sin.
Promiscuity comes to mind as an easy example.
Practicing diligence and prudence from the very beginning makes choosing the good easier. It's a lot harder to grow vegetables in a weed-filled garden than in one that is regularly stripped of the unwanted plants.