After being knocked down by the windmill, how does Don Quixote explain the fact that he has not killed a giant?

Don Quixote’s excuse for not being able to kill a giant was that a magician (or an evil sorcerer) turned the giants into windmills so that Don Quixote would lose the fight.

Don Quixote thought that the windmills were giants even though Sancho Panza told him they were not.