This trick is very well known and often done with three lines of seven cards shown face up on the table. This version is exactly the same trick, but a little disguised.  

1. Place the three piles of cards with seven cards in each face down on the table in front of the Lucky One - in this case Smidgin Ubiquitous. 

2. Have Lucky One choose one pile and then fan it for him or her, so they can mentally select one card from the pile and memorise it without you being able to see the cards. 

3. Collect the three piles placing the selected pile in the middle of the other two. 

4. Without changing the order or shuffling, deal out the three piles again, face down, dealing one card to each pile at a time. 

5. Without looking at them yourself, show Lucky One one of the piles. Ask if the card is there. If so, collect the three piles, placing the pile with the selected card in the middle of the other two. If not, show the second pile and ask, again placing it in between the other two if the card is there. If not, don't bother showing the last pile, just place it in between the other two. Any order in displaying will do, as long as the pile with the selected card is collected in between the other two. 

6. Repeat the last step once more - again ensuring the pile with the selected card is in between the last two.
 
7. The selected card will now be at the 11th position. 

8. Count out the cards from the top, face down on the table with the magic word: MATHEMAGIC.

9. Turn up the next card and it will be the selected card. Lucky One will be as amazed as Smidgin was here.

10. I wouldn't tell Smidge how it was done - so make sure you keep the secret - except from me. I want to know why it always works.

Work through this trick with the cards face up on the table and track them through ...

Then explain why it always works.
In your own words and making as much sense as you can. You might like to include a diagram.

While you are at it, can you describe how your brain goes about tracking such logic?