John Marston has become one of the most recognizable video game protagonists since his debut in 2010's Red Dead Redemption. Despite only appearing in one game at the time, his characterization was quite thorough and players learned a lot of trivia about him - but it seems something we thought we knew about John was a lie all along.

He maintained the deception for over 10 years, but recently a video posted on Reddit from Red Dead Redemption 2 has revealed the truth. All this time, we were under the impression that John Marston cannot swim - we were, however, played like a damn fiddle.
John Marston can actually swim. He lied to us... from reddeadredemption
In the video evidence, a player is shown shoving John Marston off a bridge and into a body of water - instead of drowning, dying horribly and messing up the time-stream (or just producing a mission failure), Marston proceeds to swim ashore with perfect form, too.
Naturally what we're witnessing here is just Rockstar Games' blanket NPC AI programming kicking into gear, with John Marston doing the same thing any other NPC would - rely on pathfinding to get back on the pre-scripted track, thus swimming out of the water he wasn't meant to be in.
Nonetheless, it would have been an appreciated and funny addition if players would be hit by a mission failure if they tossed John into the water - or if one of the other NPCs who can swim in the game's canon would jump in to rescue him - better yet, you'd have to throw in a lasso after good old John and tow him ashore!
Considering the emphasis these games place on their characters and level of detail, this sure seems like the sort of thing the folks over at Rockstar Games would have paid attention to - alas, it seems John Marston was lying about his inability to swim all this time. Maybe it was a clever ruse to make his enemies underestimate him?