Consider the game of 'Go' - there's a very small amount of rules, and once you know those, you know all the rules, but there is still a lot of higher-level strategy to learn. It seems bad to not know all the rules, but good to have more strategy to discover...

It would obviously be disappointing to then be playing an opponent, and discover they are about to beat you with a rule that's new to you; or to have played the game for a long time and then realise there was a move you never knew you could make. Watch someone learn about capturing en passant in chess for the first time from their opponent, during a game they are invested in...

At the same time, learning a new 'strategy' is quite enjoyable and delightful - maybe even if you learn it as an opponent beats you with it – as long as it is something you could have reasonably discovered yourself, even if you didn't. (?)

A disappointed sensation like "oh, I never knew you could do that" is bad; but "oh wow, I never realised you could do that" is good.

What's the difference between these 'rules' you should know, and 'strategies' to discover? Is there a real difference? You are ultimately just choosing an action from a constrained set of candidate actions in both cases; in one case not knowing the full action set is bad, and another it's good.

Clearly, you can think of a game at multiple different valid levels of abstraction - 'you can push these controller buttons'; 'you can move up, down, left or right'; 'you can sneak up behind the enemy'; 'stealth is the best strategy' etc. Clearly, at some levels, not knowing all the actions is frustrating; whereas at other levels, discovering new higher-level actions is delightful.

So, which is shooting the crate to find a medkit?

It's not completely clear, but I can see how people would think it is a hidden rule, something they could not have been expected to realise themselves, but which was obvious to players of other games - a missing word, rather than a delightful high-level behaviour that falls out of the interaction language the game has taught them.