The Witness is not like other games, so it stands to reason that a Witness speedrun would not be like other speedruns. (Warning: The Witness spoilers ahead.)
The Witness' island is overrun with brain-incinerating-puzzles (and statues that are just, like, SO sad). Some puzzles are hidden. Some, by their very nature, take significantly longer than others. This makes a 100 per cent completion speedrun tricky, to say the least.
In setting a 100 per cent completion record of 3:16:21, speedrunner FearfulFerret had to solve an especially involved puzzle embedded in a 58-minute film in an underground theatre. According to Eurogamer, the film is based on a GDC talk given by another game developer, Brian Moriarty, and as it progresses, an eclipse appears over the screen. That process needs to be complete before you can finish tracing a line in a nearby corridor.
"I've never waited through this before," said FearfulFerret (you can see for yourself at 16:40 in the above video). "I'm excited. I'm literally going to get in my car, drive like 15 minutes to What-A-Burger, get probably a fish sandwich -- because I had a burger for lunch -- gonna come back here, gonna eat it on webcam, and it's gonna be delicious. It's gonna be delicious."
And that is exactly what he did. It worked, and he went on to complete the speedrun.
It's by no means a perfect run, and FearfulFerret himself admitted that there's a ton to improve. At this point, however, few others have tried 100 per cent speedrunning The Witness, so his record stands. It's not unusual, though, for a specific game to have countless speedrun categories, each with their own qualifiers and hyper-specific nuances. Here's hoping "fish sandwich run" is etched into the annals of Witness speedrunning history as a rite of passage, a tradition.