In 2012, a single copy-paste mistake in a Microsoft Excel formula helped trigger one of the biggest trading losses in Wall Street history — JPMorgan's infamous 'London Whale' disaster. We dig into how a humble spreadsheet, the same tool your aunt uses to plan Thanksgiving seating, became a load-bearing wall in the global financial system without anyone really deciding that should happen. If last episode's Mars mission taught us that unit mismatches can destroy spacecraft, this one shows that a missing cell reference can apparently sink a bank.