The phantom goal against Villa without which they'd never be where they are now, nor had won a trophy in Europe without it as they'd have been relegated. It reminds me of the '11' scene from Spinal Tap.
Player - "The ball crossed the line. It's a goal."
Ref - "But my watch didn't go off to indicate a goal."
Player - " But it was a metre over the line. What did the linesman say?"
Ref - "I don't need to speak to the linesman because my watch didn't go off. It's not a goal."
Player - "But your watch failed. It crossed the line. Are VAR going to review it."
Ref - "This watch goes to 11!"
It still baffles me to this day that VAR didn't intervene in the most clear and obvious error, but they could spot Lundstram's toe one inch offside after 10 minutes of review because in the moment that was such an obvious error to everyone in the ground. Absolutely mind boggling.