There are some things you need to know as a player while playing a tabletop RPG. You need to know how the basic mechanics work and what your options are. You need to know how to build a character and how combat works so you can make reasonable decisions on engaging in it or not. What you don't need to know is exactly how the GM figures out obscure challenges like building a crossbow, holding your breath, or calculating the precise deviation between your assessment of the value of a piece of treasure and its 'actual' value. If a player happens to know these things, okay, but if they don't then the game still runs just fine.
The problem lies in making a game that has so many rules that people feel obligated to know that it drowns them in details. DnD 3rd edition skills are a great example of this in that skill descriptions contained huge blocks of information on all kinds of obscure mechanics. How often are we really going to resolve swimming checks by rolling hour by hour to see how many miles a character swims and how likely they are to drown? Do GMs actually sit down and say "Okay, so, you are 18 miles from shore, the weather is defined as choppy, lets roll some dice and see if you can make it." If it never comes up it is just wasting space in the book and boggling the minds of the players who think they should know how their skill works. A far better use of book pages and brain cycles is figuring out how to solve problems generally rather than trying to provide ready made solutions for every problem.
As I mentioned in my last post, the Amber RPG does a beautiful job in this regard. It has a few rules and then reams and reams of examples for people running the game for running skill based challenges, combats, creating things, and everything else. Players can read the first few sections to understand the basics and then rely entirely on the GM to know all of the fiddly bits. This is something I want to try to emulate in HBT, though I will of course be designing a more traditional RPG than Amber. Specifically I think I want to have a really bare bones players section that outlines all that a new player would really need to know and then an extensive section of GM strategies and guidelines. In particular I really want to give good examples of making interesting and complex Skill mechanics that push beyond the basic 'roll 1d8 and see if you win' that GMs can use if and when they feel ready.
The only fly in the ointment here is Rituals, which are difficult because they have large descriptions and which I would like a lot of. I have everything from Detect Magic to Create Volcano to Become a Carrier of a Virulent Plague and I would really like a ton of variety. Just like in DnD though if you want to have a nice variety of really interesting effects you are going to use up enormous amounts of space and it will be really difficult for players to take it all in. I remember perusing the hundreds of pages that DnD spells took up, which was perhaps too much, but also the embarrassingly tiny spell list in Warhammer RPG which had hardly any options at all. It feels wrong to be planning supplementary material before I even have my basic book all laid out...