Elements Of A Linear That Players Generally Won't Solve In Time.
I'm not a fan of the Dead Woodlouse test. However, after quite a bit of observation, some things that generally[1] don't work and should probably only be included in your linear/event plan if you've got a backup for when I was right all along:
Players in an encounter will try to beat that encounter. Making them run away - making the only way to win the game being not to play the game - isn't something that fits with the game level of the event, and won't generally come to mind. If you're planning on sending in a group of hard bastards the players will run away from? They Will Die. TPK will happen.
As the end of an event, an encounter that is _known_ to be a fighting retreat can work, the characters live to plot another day, rescue their lost friends, etc.
Even if your waves are one hit goblins who die, and the puzzle is to stand on top of where they're respawning, the players are too busy fighting or watching for the enemies to solve the puzzle, then they run out of mana/spirit/health, thus death.
It's a convention. If every NPC in the world has to establish their own bona-fides as a trustable person, then putting an NPC into play is much harder than it needs to be for a larp game to work, so NPCs get an automatic "trustability" positive value, because otherwise you'd spend half the encounter bringing in previously known NPCs to say "this is a trustworthy person", and everyone else will be killed on sight. If a NPC is working to their own ends, that's fine, but that kind of needs to be established, otherwise the character party has no reason not to treat them as something of an abstract story element, rather than a character.
The alternative is for NPCs to *be* characters with their own motives and desires, so players can always assume that any NPC is also possibly lying to them (Which is what PD do for Maelstrom and ODC), but that's a big burden for a small larp system, and generally requires a larger permanent cast.
[1] Generally is not always, in either direction. These can work, but - in my opinion and experience - generally don't.