"The Way We Was", season 2, episode 12
Early Simpsons were just fantastically well written. The show didn’t hit it’s comedy peak until about season 5, but the first few were excellent at the narrative aspect and portraying the emotional side of the characters.
This episode was on TV some time last year, and since then the line “How can the only thing I’ve ever been sure of in my life be wrong?” has stuck in my head. Even if they’re not real and yellow, it’s still heartbreaking.