Let us suppose that a certain lexical unit has been assigned to the student, introduced, but then for some reason is dropped from the active acquisi- tion process and re-introduced at a later time. In such a case, the time and effort spent by the student between the initial introduction and the tem- porary removal from the acquisition process would be, effectively, wasted. After the re-introduction, the student would need to start the learning pro- cess all over.