Christopher Nolan has finally explained the controversial “spinning top” ending to his critically acclaimed science fiction blockbuster Inception.

Speaking at a commencement ceremony at Princeton University earlier this week, the British filmmaker said the 2010 brainteaser’s final scene inspired more questions from fans than any of his other movies. So much so, in fact, that he often skipped “out of the back of the theatre” during screenings to avoid having to answer them.

The film is a heist thriller about a team of corporate spies exploiting the existence of multiple levels of reality that supposedly exist inside the minds of human beings. Inception’s greatest puzzler is its final scene, in which Leonardo DiCaprio’s Dominick Cobb successfully reunites with his children against seemingly impossible odds after pulling off an elaborate “inception” heist to convince a businessman to break up his late father’s corporation.

Earlier in the film, Nolan has established the idea that a personal totem — in Cobb’s case, a spinning top — can help establish if one is experiencing a dream or reality. If the top continues to spin indefinitely, the owner is most likely stuck in somebody else’s dreamscape. If it drops, they are in the real world.

As Cobb miraculously makes it through US customs despite being wanted for murder, it appears his employer has made good on a promise to wipe out charges against him in exchange for the spy’s services. But DiCaprio spins his top nonetheless — just in case he is still dreaming. Then the screen cuts to black before we see whether the totem topples.

The filmmaker explained that he saw the concept of reality in the film — and real life — as entirely subjective. So DiCaprio’s character doesn’t wait to see if the spinning top drops because he no longer cares to distinguish between a possible harsh reality and a potentially wonderful dream.

“The way the end of that film worked, Leonardo DiCaprio’s character, Cobb — he was off with his kids, he was in his own subjective reality,” said Nolan. “He didn’t really care any more, and that makes a statement: perhaps, all levels of reality are valid.”

The filmmaker used the spinning-top puzzler to make the point that reality and dreams do not exist in mutual isolation. “In the great tradition of these speeches [to undergraduates], generally someone says something along the lines of ‘chase your dreams’, but I don’t want to tell you that because I don’t believe that,” he said. “I want you to chase your reality.”

Nolan added: “I feel that, over time, we started to view reality as the poor cousin to our dreams, in a sense ... I want to make the case to you that our dreams, our virtual realities, these abstractions that we enjoy and surround ourselves with, they are subsets of reality.”