As a student, one of your objectives is to seek accuracy in your drawings (he called it "searching accuracy") as a means to train your reactions automatically to find form, shape, value, etc., so that when you are before nature and your enthusiasm runs rampant, along with your pencil or brush, your artistic "auto-pilot" will still give you good drawing, form, etc. In essence, I think that he was saying that as a student, you need to "over learn" your skills so that they become almost automatic, knowing that when you are "in the field" or out of school, you will be losing some of it to the "passion of the moment." By doing this, you get good draftsmanship, color, values, etc., to look real but still have the passion in the painting to keep it from looking mechanically correct.
Richard