Craig Stern of Sinister Design is writing about Unpredictability and Control in games. He says that players accept losing in real-time games as long as the controls are tight. But losing to a bad roll of the die (or random number generator) is less acceptable. Quote: "Thus, although randomized results create uncertainty, they can also sabotage the sense that a player is responsible for her failures, which is bad."

In my opinion there is too little randomization in MMORPGs. They are nearly totally deterministic. Before combat even starts you know what the monster will do, and what keys to press in which order to optimally defeat it. Thus combat involves no thinking, only execution.

As Craig Stern says, the solution is not making the result of button presses unpredictable, but to make the opponent unpredictable, or the starting situation. That is why card games work: The cards you draw are random, but what you can do with them is not. And in a MMORPG the monsters could be made more unpredictable as well. Why do people need to know in advance what the boss mob is going to do after X minutes to beat him?