Resistance

Above I wrote about "resistance", and this basically is too a good way to express how a UI interacts with a player. It expresses the problems or conflicts the player meets when converting his thoughts to the game actions. If the thinks "left" for example and the player atually has to click right/press right, this is a conflict for the player to which he first needs to adapt. Some games use this consciously to add another twist to the game (eg. When collecting a special "bad" item), but generally a UI will be designed to have a harmonious relationship with the player. But conflicts can basically cannot be avoided in a game that is complex to a certain degree and interacts with a complexity of a human being! IT is always best to take yourself as model at the start, since you are much more human than any created image could possibly be in your head.

A way to optimize a given UI is to actually take a look at how the player has to perform the different actions of the game, by using a programming language for example. This way you are also able to see how mechanically/thinking intensive the game is, and where the biggest problems arise. If you have a working version of the game though, it is always best to just play it of course, and this phase might be skipped, except you want to take a very detailed look at what is really going on ( or should be going on ) inside the player.

Summary