I kind of get the marking thing, as far as how the rules explain what it does, but how exactly does it work?
I mean, so a Fighter or a Paladin marks someone. So what? I can see it as a term similar to how 3E Dodge has the person choosing the target that the feat works against. But how or what is it exactly in the 'marking' that causes the target to suffer a penalty to attack?
Fighter: Aha! I just marked you!
Monster: So what? **Whacks rogue flanking him**
Fighter: You have to attack me.
Monster: Why? **Pummels paladin coming over to surround him**
Fighter: Because I marked you. If you don't, it will be harder to hit anyone else but me.
Monster: Hmmm, how exactly? I mean what exactly would cause me to miss someone else rather than hit you? **Lands two-weapon attacks on the paladin and rogue**
Fighter: Well, the mark just does it. That's why its called a 'mark'.
Monster: Oh...ok. Good luck with that!