If the game director and producer have just one job that matters it's to ensure that the entire team heads in a single direction, staying on course throughout the years-long development process. To that end, I drafted a set of rules, "The Deus Ex Rules of Roleplaying."

Here's the list of rules, the mission statement for the game:

• Always Show the Goal - Players should see their next goal (or encounter an intriguing mystery) before they can achieve (or explain) it.
• Problems not Puzzles - It's an obstacle course, not a jigsaw puzzle. Game situations should make logical sense and solutions should never depend on reading the designer's mind.
• Multiple solutions - There should always be more than one way to get past a game obstacle. Always. Whether preplanned (weak!), or natural, growing out of the interaction of player abilities and simulation (better!) never say the words, “This is where the player does X” about a mission or situation within a mission.
• No Forced Failure - Failure isn't fun. Getting knocked unconscious and waking up in a strange place or finding yourself standing over dead bodies while holding a smoking gun can be cool story elements, but situations the player has no chance to react to are bad. Use forced failure sparingly, to drive the story forward but don't overuse this technique!
• It's the Characters, Stupid - Roleplaying is about interacting with other characters in a variety of ways (not just combat… not just conversation…). The choice of interaction style should always be the player's, not the designer's.
• Players Do; NPCs Watch - It's no fun to watch an NPC do something cool. If it's a cool thing, let the player do it. If it's a boring or mundane thing, don't even let the player think about it - let an NPC do it.
• Games Get Harder, Players Get Smarter - Make sure game difficulty escalates as players become more accustomed to the interface and more familiar with the game world. Make sure player rewards make players more powerful as the game goes on and becomes more difficult. Never throw players into a situation their skills and smarts make frustratingly difficult to overcome.
• Pat Your Player on the Back - Random rewards drive players onward. Make sure you reward players regularly and frequently, but unpredictably. And make sure the rewards get more impressive as the game goes on and challenges become more difficult.
• Think 3D - An effective 3D level cannot be laid out on graph paper. Paper maps may be a good starting point (though even that's under limited circumstances). A 3D game map must take into account things over the player's head and under the player's feet. If there's no need to look up and down - constantly - make a 2D game!
• Think Interconnected - Maps in a 3D game world feature massive interconnectivity. Tunnels that go direct from Point A to Point B are bad; loops (horizontal and vertical) and areas with multiple entrance and exit points are good.

That was it - we could build most of a game (at least a Deus Ex game!) simply by assessing whether a map or game situation met all of these criteria - and it WAS all of them, not some! Still, these rules were created before we ever wrote a line of code, created a piece of art, recorded a sound or built a level.​

“SAM” stands for “Setting : Avatar : Mechanics.”

Setting, Avatar and Mechanics are all on sliders, with “none” at one end and an arbitrary “maximum” at the other.

Setting and Avatar are pretty straightforward and, as in most media, they can be of some or no importance. In other words, it's possible to make a game with no setting or player avatar. In yet other words, you can have a SAM of 0:0:X

But let's look at that “X” - Mechanics, can't be taken down to zero in a game. Given that, it seems clear that game design and development must begin with core mechanics. Nothing else differentiates us from other media. “X” has to be > to 1.​