I recently asked a question and got a great answer that involved proving that "X is almost surely one of the roots of P".
I know (now) that "almost surely" means "with probability 1", but I've never understood why that phrase exists.
When something has a probability of 1, it's going to happen, no almost about it. What's the story there? I've tried looking this up online, but I just got more definitions, not meaningful explanations.