Englishdaydreamer
noun
David was sacked from his very first job because he was a daydreamer:
dreamer, fantasist, fantasizer, romantic, romancer, wishful thinker, pipe-dreamer, castle-builder, Walter Mitty, idealist, impractical person, unrealistic person;
visionary, theorizer, utopian, Don Quixote;
rare fantast, reverist.