It's not like we doubt the Kate Bush magic, but...
Max Mayfield is one of the few lucky people who managed to survive after being cursed by Vecna: mainly due to her friend's awareness on her music taste and the power of 'Running Up That Hill' by Kate Bush.
Or was it about something completely different? Now that we know Vecna's gruesome origin story, there might be more to Max's miraculous escape than we initially thought.
When Max hears 'Running Up That Hill', happy memories start to flow in her head, helping her to overcome fear and guilt fueled by Vecna's curse. Among the many flashbacks we see her and Eleven hanging out in the mall – and apparently, so does Vecna.
"Didn’t even realize that Vecna probably saw El in Max’s memories and that’s why he let her run away… that’s why they said he looked surprised," @herbodys.
Vecna is no stranger to Eleven: it was she who banished him into the underworld when he, still Henry Creel aka 001 and not a twisted zombie-like creature, tried to manipulate Eleven into joining him in whatever gruesome things his mind was up to.
So perhaps seeing Eleven in Max's memories took Vecna by surprise, which is why Max had the chance to break free and rush back into the real world.
However, some fans beg to differ.
"Vecna probably already knew about El in S3 though. When Billy was possessed and found out El was the one w powers, he had to report back to the MF (flayer). they had a brief conversation about she almost killed him, but she wouldn’t be able to stop them," @EARTH2MAU.
Still, the extent to which Vecna is connected to Mind Flayer and the Demogorgons remains unclear. We are not even sure that Vecna's red underworld lair is the same thing as the Upside Down, so there might be space for other fan theories – at least until we get to see the finale.
Volume 2 of season 4 drops on Netflix on July 1.