5.) The cake is a lie
Here's another instance where an integral phrase in a video game became so popular in gaming culture. Some people have even heard of "the cake is a lie" before they knew about Portal's existence. While I don't think that the twist is earth shattering per se, knowing its meaning beforehand ruins what made it so special to being with.
The protagonist is promised cake as a reward for completing all of the puzzles in the test chambers. However, players quickly realize that the promise of cake was indeed a lie when Chell is forcefully maneuvered to a pit of fire. Throughout the game, players see graffitis of "the cake is a lie" to express the dishonest nature of the test.
Consequently, it's not primarily the absence of cake that makes this phrase memorable. It signifies the revelation of something deeper than what most players thought this game to be and that's something players should experience themselves.
When someone asks you why the cake is a lie? Don't tell them why, just tell them to play the game.
