Well I can look at some of these stats and associate them to other games and I will focus mostly on the similarities to World of Warcraft. Agility is one that is common in a lot of games. World of Warcraft uses Agility to effect your weapons strength and your resource recharge rate (which so happens to be Energy). In Destiny I can see Agility being used for movement speed since this is a FPS. Although, movement speed is going to have a greater use in a FPS genre so I'm cautious to think if there might be some other effects to it. Maybe a hard cap on how fast you can move so that it doesn't look ridiculous. Also, Agility could effect jump height which I think is completely logical in a FPS where environment is used more than in say a World of Warcraft. Discipline is not normally used but has popped up in a few games. Destiny's take on it might have an effect on accuracy and haste for spell casters (think cast speed and how accurate you can hit targets). This is assumption of course but it sounds like a logical choice. For gun wielders, think about how quick you would reload and how steady you hold the gun. Just the word Discipline makes me think of snipers more than spell casters, but I could be wrong. Shields seems a little simpler, you have a Titan class that may be like a tank so having block abilities or absorb effects could be possible. Shields would shine here. There has also been talk about having spaceships. Think about shields there too. I could see a Titan wanting Shields and Discipline (think large absorbs and discipline could effect the recharge rate of those shields. Energy feels like a spell caster stat to me. Think power, mana, and rage. All classes probably have energy, but the classes might have different pool sizes. Another route could be a static pool size for all classes and different energy costs for each ability alongside what class you play. I am going to use a generic ability, lets say teleport is an ability in the game. The more energy you have may allow you to teleport two or three times before you run out of energy. If you have low energy maybe you can teleport one time then you are done. Another example might be if you are a warlock and you shoot fireballs, well with high energy those fireballs might hit harder. Maybe energy ties in with shields. Say a Titan as low shields but high energy. That may look like a Titan that is constantly shield but the absorb amount is low which means he absorbs partial damage, so he will have to reapply the shield more often. That could be for a Titan that wants to play more offensive rather than defensive. There are a lot of ways Bungie can take the stats. Let's just hope it's the best way (I have no clue which is the best way).