I remember I correctly guessed the twist at the end of the old show Dead of Summer back in 2016. After it aired, there was an interview with the producers where they said no one had guessed that, and I wished that I'd shared my guess at the time (I didn't want to be That Person who's always wise after the event. Having dated That Person at university, where he'd always say "I always thought there was something off about So and so" when he hadn't at all, I knew how irritating That Person is.)

To this day, I wish my guess for the ending of The Flash Season 5 had been what we got - I was convinced that Eobard was going to manipulate Nora into giving Barry the metahuman cure, and the finale was going to be Nora having to try and fix the timeline which she'd broken by doing that. Who cares about Cicada anyway?