I watched Tenet and then some YouTube videos “explaining” it. I realized something. It’s Bill and Ted. (Spoilers?)
In the First Bill and Ted’s, they’re breaking out all their historical friends from jail and Ted’s father confronts them. Ted says, “Garbage can. Remember a garbage can.”
Then BOOM! A garbage can falls from nowhere and they escape. So obviously they finish what they’re doing and then go back to that moment to drop a garbage can on the dad’s head.
Tenet is one big sequence like that. They’re on a mission and realize that something different needs to happen at a specific moment so they yell, “Garbage can” over and over again so they know when to come back to specific moments to help themselves out.