I wrote out the 4 possible coin flips and expected to try to work it out more or less by brute force but once I looked at the possibilities the answer came to m

I wrote out the 4 possible coin flips and expected to try to work it out more or less by brute force but once I looked at the possibilities the answer came to me and seemed obviously correct at once. Brains are weird. Just because I am one doesn't mean I have the faintest clue why or how it does things.