While not all of OSR is rules-light or rules-minimalist, a lot of time it's rules-expectant. That is, if there are few rules, so you should follow all of them. I recently came across a few situations that bothered me.
The first is buried in this video:
https://www.youtube.com/watch?v=LfBYu-ry6bs&ab&ab
For brevity's sake, at one point a Dwarf stands on cracked dungeon floor without being made aware of said floor. There is no point where the dwarf's innate stonecunning ability is mentioned (in spite of it existence since 0E). That means to put it simply, this GM fucked up and didn't account for it, and almost killed a character because of it. Killing characters is fine if they earn the death. A Dwarf shouldn't have to call for a check if you're a GM paying attention and are using something that's well within the Dwarf's stonecunning wheelhouse. The GM sprung the trap, so he was paying attention. Therefore he fucked up.
The second was in a Mork Borg game I attended.
I and two compatriots were fighting five evil kobold-ish sorcerers. I killed the leader. In Mork Borg that means a Morale roll is rolled. It wasn't. We then killed half the force. In Mork Borg that means a Morale roll is rolled. It wasn't. Then we brought the force down to one person with 1/3 or less of it's HP left. In Mork Borg that means a Morale roll is rolled. It wasn't. No explanation was given. Morale is one of the four stats Monsters have in Mork Borg, making it one of the most important pieces of information in regards to tactics and generally dealing with monsters in any way. Not rolling morale is eliminating one of the few tactics in the game.
When there's like 10 rules in a game, you need to know them all to effectively GM the game. This was some weak sauce with killer consequences.
