What it is
A claim is falsifiable when it says what observation would prove it wrong. Karl Popper made this the line between science and everything else: if no possible evidence could count against an idea, then no evidence really counts for it either.
“Everything that happens confirms my theory” sounds strong. It’s actually a sign the theory isn’t saying anything.
How it shows up for me
I use it on myself most. When I’m sure about someone’s motives, I ask: what would they have to do for me to change my mind? If the answer is “nothing,” I’m not reading them, I’m writing them.