Consider my example from earlier --> sometimes units would be greyed out, and the game would tell you what you need to build them. Other times, a unit you could train if meeting the requirements would not appear in the city at all. "Which units player is allowed to build right now" is a dictionary-defined example of a rule in Civ 6. Once we get past things like that, the title is something of a misnomer, but misrepresenting outcomes/costs is still a big problem in a strategy game (and most other game genres). If an unspoiled player can only learn information about mechanics (not variable in-game situations) from 3rd party sources or trial and error you have a poorly designed/implemented game. It's an example of fake difficulty (trial and error gameplay and/or outcomes not reasonably determined by player actions/choices). Variable in-game situations (such as what an opponent is doing) intentionally provide incomplete information. Even if you know about everything in the game, you still wouldn't know some of what other players are doing w/o cheating. This is the only information a well-designed game would hide and/or fail to provide.