Imperfective aspect doesn't imply the action wasn't completed, it just doesn't focus on this action as a certain point in time with a certain result. More as a repeated activity, or a prolonged activity that "was taking place" for some time. Also it is used to refer to action in general, i.e. when you ask questions whether some activity was there at all, or not, you use imperfective ("Ты читал эту книгу?" is a good example)