Thorndike's Law of Primacy

Things learned first create a strong impression in the mind that is
difficult to erase. For the instructor, this means what is taught must
be right the first time. For the student, it means that learning must
be right. “Unteaching” wrong first impressions is harder than teaching
them right the first time. If, for example, a student learns a faulty
technique, the instructor will have a difficult task correcting bad
habits and “reteaching” correct ones.

The student's first experience should lay the foundation for all that
is to follow. What the student learns must be procedurally correct and
applied the very first time. The instructor must present subject
matter in a logical order, step by step, making sure the students have
already learned the preceding step. If the task is learned in
isolation, is not initially applied to the overall performance, or if
it must be relearned, the process can be confusing and time consuming.
Preparing and following a lesson plan facilitates delivery of the
subject matter correctly the first time.