Everything should be attainable. Well, at least in videogames. One of the problems that's become more and more apparent in games is the fact that there are things in the game that are practically impossible to find out when playing.
My philosophy is: A player should be able to get everything in the game by figuring out things -in the game-. I don't mind the cheat code here and there, but that's a bit beyond the scope of what I'm getting at. Ultimate weapons, hidden summons, super items, whatever...there should be some sort of hint in the game that lets the player find these items. Sure, there can be some sort of insane trial standing in the player's way, but as long as the player was able to determine where the item is by clues found solely in the game, it's good.
I know that I've played games where you've had to do some little thing in the beginning of the game that reflects on something later in the game, which ultimately results in the loss of an item of some importance. It's an optional item of course, but without a strategy guide of some sort, there was no way I would have ever known it was there. I don't want game companies adding extra content into a game where the only way I'm going to find it is if I go online or drop $20 for a strategy guide. Hell, even the newest incarnation of FFXII has a weapon that is linked to some random chests located in the beginning of the game. I've already passed those up, not knowing anything about it, and now I won't be able to get the item. Whether or not I had planned on using it is irrelevant.
So listen up, developers. Stop adding content that can't be found by only in-game info! I want to get the most out of my game. I want to explore every nook and cranny on my own, and if I miss something, I want it to be because I missed some clue, not because no clue existed in the first place!