Good input leads to good results. Bad input leads to bad results. This isn't something that's true about games, it's true about most things in life. Sure, there are some strange times where bad input accidentally leads to good results - the people who follow up on why their assessment of the quality of their inputs was wrong are the people who make all sorts of wacky discoveries.
But that's a bit of a digression. The point is, in most games, when you do the right thing, you're rewarded. Mario jumps on the mushroom, and an obstacle is cleared. If he fails to jump at the right time, he's likely killed, resetting the player to the start of the level. Most games have this sort of punishment for failure - whether it's the limited life scheme of old-school arcades, or reset to a checkpoint a'la Halo, the punishment for failure in most cases is death. This is a paradigm that has existed in videogames from their very inception. Spacewar has this risk-reward balance exactly.
And then there was Wii Sports.
In Wii Sports, if the game doesn't know what to make of your input - if you're swinging the Wiimote around haphazardly, instead of bowling properly, the game tends to interpret it as successful input, and behave like you told it the right thing to do. Try it - next time you're bowling, instead of "bowling" properly, swing the Wiimote in a completely arbitrary way. You'll find that a huge portion of the time, your ball will still go mostly down the lane, and probably even hit a couple pins, if not strike altogether.
The first time this happened, my wife's younger brother showed us how to "break" the game by swinging in a completely oddball way. Nothing like bowling at all, but he nearly doubled our scores, and we'd been trying to "bowl" legitimately the entire time. At first, this seemed like a glitch - some exploit he'd found, and in a way, it is.
With most traditional games, input is binary - you either hit the button or you don't. Sure, there's "analog" input on the sticks, and all sorts of strategic decisions you can fail, but the core mechanic for most games is that you either hit the button, or not. With motion control, everything becomes a lot hazier. There isn't a single "right" input - how you hold the controller changes the input. How long your arms are, or what degree your wrist is twisted in your natural relaxed position... all these things affect the specific input of a motion controlled game.
How, for instance, in Wii Sports, can you really quantify every part of a bowler's pitch? It boggled my mind, originally, when it "felt" so right - but the simple fact of the matter is that they don't actually read all that much input from the swing - it's mostly a very limited set of inputs that they check, and they assume everything that they're *not* checking is going well.
Because everything that's important to the gross motion of the bowling swing reads right - because the output feels like a natural extension of the input under normal conditions, most people aren't going to question specifically which input is being taken in. Enough, it seems, to understand what the player is doing correctly. Not so, I'd say. Not at the edge cases. Not during the weird swings - things that would normally be considered failure states.
Now, it was undoubtedly a conscious decision on Nintendo's part to bias the game toward interpreting uninterpretable input as "good" rather than "bad" input. But the repercussions are astonishing. Wii Sports is a spectacularly inclusive, accessible game. People can jump right in, and feel like they're doing well. Imagine if they'd biased the game towards the traditional failure? The first few times you'd bowl, you'd gutterball, or miss all the pins. Your first experience with the console wouldn't be one of success and joy, marveling at how the console interpreted your obviously wonderful bowling motion for what it was, but instead, a feeling of misunderstanding, failure, frustration, and defeat.
This kind of reward isn't limited to Wii Sports - a lot of casual games bias the player towards success. Peggle's a good one. There's no way that anyone is making judgements about the fifth bounce of their ball in that game (a weird mix of pachinko and Puzzle Bobble), but that randomness tends to work out on the player's behalf. Bejeweled is the same way. There's strategy involved, but no one's making 8-chain combos - they just happen periodically as a random reward to the player. Is it a result of random gem generation? Maybe. Maybe not. The point is, it makes the player feel successful, rewarded, and happy, even if they really had very little control over it. They gave the game input - good or bad, and it tended to reward them with something.
I think it's interesting to note how few other console games (even on the Wii) actually bias the player towards success. So often, the punishment for bad input is failure, which just leads to frustration, irritation, and anger. It requires a huge amount of finesse on the designer's part to keep that level of frustration low - to make the player feel like it was their fault for failing, instead of the game cheating them out of success. But there's one really straightforward way of making that frustration disappear. Bias the player's input towards success.
I'm not going to say that all games have to be "fun" - some games are about giving very controlled, "right" input. Mario is the classic example - remove the challenge and you remove what the game *is* at its core. But there are a lot more games that could benefit from learning how to turn bad input into good results, or at the very least, bad input into good input. Encouragement is a good thing. For many years, games have responded with the stick. It's time to learn how to respond with a carrot.