Anian raised a good point about the limited number of solutions for a given problem in a game - most commonly just one. Of course, giving more options is problematic, because different solutions could mean the story branching out, and it might be hard to get it back on track (if, for example, you used -- and effectively lost -- an item that you were supposed to use later on). But to use the example with the towel -- what if you had the option to transport the water with your hands cupped? Or -- just hypothesizing -- a skullcap? Or, say, the Holy Grail that you just happened to find. That wouldn't destroy those items -- and the towel that you didn't use could be used to dry the Holy Grail before putting it back into your inventory. Another example: why do you need a key for a door? Even the most rickety, termite-ridden bunch of planks, barely nailed together? Wouldn't it be more intuitive to just kick them open? I know, I know, it's an adventure game, and you're supposed to think harder than that -- but let's say there's a timer inside the game's code, and if you haven't found the key in 30 minutes, the game would let you just kick the door in.