Go there and watch that video before you read.
Anyhow, the video is a meant to be a test/demonstration of selective attention. That is, in a given situation, our minds often ignore and completely blot out things that they do not expect to see, especially when our attention is focused elsewhere. About 50% of people do not actually see the gorilla in the video. It doesn't have anything to do with profession, peripheral vision, or anything like that; people just sometimes don't see it.
I brought that up because this basic thing happens all the time in Smash, particularly in doubles. Things that you do not expect to see will completely blindside you, to the point that you might not even realize they happened at all until it's too late to deal with them. Ever lose your jump and fall all the way to the bottom of the level before you realize it? You hit jump, nothing happens, and instead of anything else registering in your brain, you just watch yourself fall? Or maybe you thought you would grab on to the edge of the stage, so you just watched the edge. Somebody else got it first though, and you just stared while you plummeted off-screen. Technically, you were looking right at your character, but you never even saw it happen.
A fun example from playing with one of my friends: the very first time I used a Captain Jack grab with Mario (you know, canceling a dash attack with grab so that you hear the "Wa-hah!") he literally stopped playing. He was grabbed. But his brain was trying to tell him, from the sound cue, that he had been dash-attacked. He did not realize that he was being held, and just kept trying to see where the dash-attack was. (Afterwards, he thought this was so funny that all I had to do to beat him with Mario was send him into laughing fits by CJ grabbing)
Selective Attention--and more specifically, any inherent expectation you have regarding the match--is a liability. Like any liability in a multiplayer game, you can use it as a weapon. The most commonly used form of it that I know is the empty jump.
Tournament players learn to SHFFL aerials. It's just a thing that you learn unless you're playing one of like, three characters that don't really utilize it. Peach, Samus, and... Yoshi. I don't know.
Point is, you learn SHFFLing. You come to believe that anytime somebody is in the air, especially if they're against your shield, that they're going to do an aerial. So you watch for it, so you can shieldgrab, or roll away, or up+b out of shield, or whatever. And you watch. And after awhile, you become so conditioned to seeing the aerial that you won't realize it if the other guy doesn't do an aerial at all. You'll just keep waiting. By this point, he's landed and grabbed you. At this point, you might finally notice, but odds are you won't even DI the throw. Or, in the ICs case, mash out before I infinite you.
Another example: using the ICs d-throw d-air on Fox is kind of risky, because he can smash DI and then buffer a roll to get away. It's escapable, and can be a waste of a grab if the other guy knows how to get out.
But what if you know they're going to roll? http://www.youtube.com/watch?v=gGq7X37ypEA#t=1m05s
In this case, Forward SDI's away and down, then rolls like you're supposed to, and I take a big risk in just dashing towards his landing spot. I d-smash him, and he DIs with it. Note the percent; grab at 30 percent, dead at 61% because he can't recover.
Forward's a good player with pretty decent reaction time. What makes somebody like that DI badly? I'm willing to bet that, because after a d-throw d-air, Popo is *supposed* to go for a grab, he didn't even realize that I hadn't done it until it was too late. He may not have even really seen me dashing towards him, or at any rate he didn't process it. The only way you can get a very good player to make errors like that is by doing things you shouldn't, and being where you aren't supposed to be. Wavelands are very useful for this for the same reason an empty jump works; you're supposed to do something in the air, and you're certainly not supposed to slide all over the place.
When does this sort of thing not work? If the other guy has a plan of action that counters your trick *as well as* the thing he expects, he might just go ahead and do it anyhow, and have it work out. An empty short hop doesn't work against somebody who uses up+b out of shield anytime you get close, because... well, he'll just up+b.
Kind of a short post, but it was something I thought of today when I read about that video and test.