What does it mean to be quixotic?

Quixotism is the universal quality characteristic of any visionary action. Acts of rebellion or reform are always quixotic because the reformer aims at undermining the existing institution in order to change it.

Who was the original quixotic? Don Quixote (hence the word).

Often held up to ridicule, frequently destroyed, the quixotic individual has been responsible for many great deeds in history, and conversely for many misdeeds, as Cervantes shows Don Quixote is responsible for the sufferings of poor Andrew.