Sir Walter's maxim applies well to himself at least, and an analysis of his powers as a critic derives some light from it.
The thing that is waiting to be said is of course that his criticism is distinguished by common-sense.

Whether common-sense should really predominate in criticism might perhaps be debated; the quality indicates, indeed, not only the excellence but also the limitations of his method.

For example, Scott was rather too much given to accepting popular favor as the test of merit in literary work, and though the clamorously eager reception of his own books was never able to raise his self-esteem to a very high pitch, it seems to have been the only thing that induced him to respect his powers in anything like an appreciative way.[19] His instinct and his judgment agreed in urging him to avoid being a man of "mere theory,"[20] and he sought always to test opinions by practical standards.
More or less connected with his good sense are other qualities which also had their effect upon his critical work,--his cheerfulness, his sweet temper and human sympathy, his modesty, his humor, his independence of spirit, and his enthusiastic delight in literature.

That his cheerfulness was a matter of temperament we cannot doubt, but it was also founded on principle.

He had remarkable power of self-control.[21] His opinion that it is a man's duty to live a happy life appears rather quaintly in the sermonizing with which he felt called upon to temper the admiration expressed in his articles on _Childe Harold_, and it is implicit in many of his biographical studies.