I'm So Good-itis

When someone is new to a game and gets really good RNG, so they think it's all skill not luck.

Especially big in singleplayer games since no one is there to trash talk.

Person 1: "Jim just got to gold rank yet he just started playing last week"
Person 2: "Have you seen the way he plays? All luck, no skill. Bet he's feeling "I'm So Good-itis" right now.