quixotic

not sensible about practical matters; idealistic and unrealistic

Like Don Quixote; romantic to extravagance; absurdly chivalric; apt to be deluded.

Spanish 'quixote' from Cervantes' Don Quixote

“That I was not discovered was due to a certain quixotic twist in my father's character.”

— Winston Churchill, Project Gutenberg Complete Works of Winston Churchill

“The character of Don Quixote became so well known in its time that the word quixotic was quickly adopted by many languages.”