What does the phrase the cake was a lie mean?

Answer 1

Because people are motivated by rewards. If you want someone to do something there needs to be an incentive.

Another answer:

"The cake is a lie" is a phrase from the video game "Portal" available for PC, X-Box, PS3, etc. Through the process of the game, a computerized female voice tries to persuade the player to give up, promising the reward of a cake. Of course, the cake is a lie.

The Enrichment Center is pleased to present an amusing fact:

"The cake is a lie" is an actual phrase, meaning "what is promised to you is merely a false motivator." Portal only popularized this already existing metaphore.