Sentence:  Ralph Wiggum is generally employed as a bottomless fount of glorious non sequiturs, but in “I Love Lisa” he stands in for every oblivious <WSD>chump</WSD> who ever deluded himself into thinking that with persistence, determination, and a pure heart he can win the girl of his dreams. 
Meaning of the word marked with <WSD> tags:  A gullible person; a sucker; someone easily taken advantage of; someone lacking common sense.