You then had to stare into the eyes of the genie (a simple comic avatar) for 20 secs mind you, and the genie asked you next to scroll down the page and find the answer.
Could the genie ever have guessed the right card you had memorized? Sure thing. Each and every time you done the trick. Jeez! How come?
Curious thing, when I first looked at the original set of cards, I couldn't help but notice that the cards they selected were pairs of same numbers but with 2 of the 4 card signs. You had for instance the 7 of diamonds and clubs but not of spades and hearts. Same thing for the 6's. Hearts and spades alone, not the remaining two, clubs and diamonds. 8s were just like sevens. At the time, I didn't suspect yet that this was the clue for the solution. This is not a hard problem to solve. Let me tell yah why.
You pick a card, say 7 of diamonds, and 'stick' it in your memory. At that particular moment, you will obviously focus on the card you selected alone and nothing else, right? The rest are still there, you might have even observed by accident that they were 8s and 6s with two signs each, but you didn't bother to remember what those signs were. You only had to remember 7 of diamonds, right?
In the meantime, the Genie has been keeping you busy with BS like "keep looking at the avatar for 20 secs" and more useless insanity like that. Its purpose was to make you defocus from the first set of six cards and make believe that the genie had some extraordinary powers to guess your selection.
Again, the clue of the story is that the only card any normal person would remember by the time he/she got to this point would be the one he/she picked initially, the 7 of diamonds, right? At this point he/she ASSUMES the other cards shown in the set were the same cards that were shown in the original set, right?
As a matter of fact, that's totally WRONG! Because the smart cookies who deviced the trick knew all this about the human mind. Focusing and only remembering his/her selection, and assuming the rest of them cards remained unaltered. Well, I am sure there are 'sick' minds out there who I believe got it right the first time. The fact that not a single one of the 5 cards appearing in the second set is identical to any of the cards in the original set! So, no matter which card you picked from the original set, you'd still not gonna be able to find it in the second set.
What have we learned today, class? First and foremost, that the human mind is bleedin' lazy, that's a fact! It assumes far too easily and in a heartbeat. We trust the genie 100%, and we're ready to believe there is some supernatural magic, rather than simply think the genie was full of shite. At the end of the first round the genie invites the naif reader to start again by uttering: "Scary, ain't it?". You feel like an idiot and try again, and again, while the genie guesses correctly the outcome each and every time. Holly shite! You look like you just discovered your braincells were made of hay.
Now, double digit IQs may spend a lot of cycles wondering about the 'secret'. Basically, you can guess someone's IQ by counting the cycles that he/she needs to figure this out. Cool shit, innit? Do this test upon your in-laws and have some good laughs. You can even shoot their portraits while they are doin' it and send them to me to post in my 'world's leading idiots' Flickr set...
The number of times I told my staff to assume nothing, especially those dreamy salesmen of ours fantasizing about a slum dunk deal based on shedloads of wishful thinking... I used to hang banners on their office walls:
ASSUME means you make an ASS of yoU and ME! or,
DON'T EXPECT! INSPECT!
BTW, there's an excellent replay of a Magic Show on BBC iPlayer if you can get hold of it. Called Derren Brown: An evening of Wonders.
Well?! THAT is scary!