Yes, never underestimate how dumb anyone (even you and me) can be.
I mean ask anyone in tech support for funny (or hand banging) examples. And yes even something really really, really, really obvious needs to be explained. Like "gold is used to buy stuff". It sounds dumb, but really, it's not. A good dev and a good design both take this into consideration when making a game. Kerberos never did unless the players complained first though. Unless, of course, the point of the game itself is to understand its mechanics. But it's kind of rare.
Also, "obvious" is kind of relative. My first kid will soon reach 3 years old. Somehow he made me realise how what is supposed to be "obvious" is really the result of years of learning...