This article contains Avengers: Endgame spoilers.

As it says on the death screens of various military first-person shooters, “‘If you know the enemy and know yourself, you need not fear the result of a hundred battles’ – Sun Tzu’s The Art Of War.” But what about when your enemy is yourself? Not in a figurative “I’m my own worst enemy” kind of a way but in a far more literal “I’m my own worst enemy and I’m coming at me with a Samurai Sword” kind of a way?

Knowing how to win such a battle is a journey through philosophy, causality, self-knowledge and fighting dirty, but it will also require some Avengers: Endgame spoilers, The Lego Movie 2 and more. I mean, sorry, but this headline and the fact this article features Endgame spoilers might in itself be considered a small spoiler, in that now you know somebody fights themselves in the movie. Sorry, there was no way to avoid that, but if you turn around and leave now you can avoid compounding the damage.

To be clear we’re not talking about fighting a robot double, a la Bill and Ted’s Bogus Journey or the Sarah Connor on Sarah Connor violence of Terminator 2: Judgment Day. We’re also not talking about shape-shifting aliens that only look like you, such as Marvel’s Skrulls or Loki, the Thing from The Thing or Mystique doing her best Wolverine impression in X-Men.