1
general::
Phrase(s): tilt at windmills
Fig. to fight battles with imaginary enemies; to fight against unimportant enemies or issues. (As with the fictional character, Don Quixote, who attacked windmills.) • Aren’t you too smart to go around tilting at windmills? • I’m not going to fight this issue. I’ve wasted too much of my life tilting at windmills.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Engage in conflict with an imagined opponent, pursue a vain goal, as in Trying to reform campaign financing in this legislature is tilting at windmills. This metaphoric expression alludes to the hero of Miguel de Cervantes' Don Quixote (1605), who rides with his lance at full tilt (poised to strike) against a row of windmills, which he mistakes for evil giants.
American Heritage Idioms