If you are imprudent, you do not use good sense. You do not look ahead at what might go wrong, and you go on anyway. We say it of people, and also of the things they do: an imprudent loan, an imprudent remark, an imprudent trip with no water. The feeling is “you should have known better,” not “you were unlucky.” It is a careful, slightly formal word. In everyday talk most people say careless, unwise, or “that was not smart.” Reckless is wilder: you often saw the danger and still rushed in. Imprudent is quieter. The mistake is that you did not stop to think, or you thought poorly. Teachers, lawyers, and newspapers still like it because it judges the thinking, not only the mess that followed. Though actually, people also use it when they simply dislike a choice. Then it is less a fact and more a scolding.