"About the ass," we are told, "Don Quixote hesitated a little, trying whether he could call to mind any knight-errant taking with him an esquire mounted on ass-back; but no instance occurred to his memory." We can see the whole scene at a glance, the stolid unconsciousness of Sancho and the perplexity of his master, upon whose perception the incongruity has just forced itself.
This is Sancho's mission throughout the book; he is an unconscious Mephistopheles, always unwittingly making mockery of his master's aspirations, always exposing the fallacy of his ideas by some unintentional ad absurdum, always bringing him back to the world of fact and commonplace by force of sheer stolidity.
By the time Cervantes had got his volume of novels off his hands, and summoned up resolution enough to set about the Second Part in earnest, the case was very much altered.

Don Quixote and Sancho Panza had not merely found favour, but had already become, what they have never since ceased to be, veritable entities to the popular imagination.

There was no occasion for him now to interpolate extraneous matter; nay, his readers told him plainly that what they wanted of him was more Don Quixote and more Sancho Panza, and not novels, tales, or digressions.

To himself, too, his creations had become realities, and he had become proud of them, especially of Sancho.

He began the Second Part, therefore, under very different conditions, and the difference makes itself manifest at once.
Even in translation the style will be seen to be far easier, more flowing, more natural, and more like that of a man sure of himself and of his audience.