What techniques are being used here to influence the subject to pick a certain outcome?

Summary of the Video: (can skip if you watched it)

The only audio is "elevator music." There is a man who communicates only with written orange signs. He asks the viewers to quickly perform some easy arithmetic calculations, and he shows the answer to each one after a few seconds:

$5+3 \ \ = 8$

$9+2 \ \ =11$

$10-6=4$

Then, he asks the viewer to quickly pick a number between $5$ and $12$. At this point, I suddenly felt a sense of urgency, and rapidly picked $7$; it was the only number I could think of in that second. Of course at the end of the video, the man guessed that the subject picked $7$.

Question:

How does this video influence the viewer to pick $7$? More generally, what techniques do these types of videos employ to try to manipulate the subject into chosing a certain outcome?

I tried to look for certain patterns in the calculations and I found a diagonal symmetry, but I'm not sure if it's relevant:

$\color {red}{\text{odd}} \ \ + \color {red}{\text{odd}}$

$\color {red}{\text{odd}} \ \ + \color {blue}{\text{even}}$

$\color {blue}{\text{even}} \ + \color {blue}{\text{even}}$

I've also noticed that the average of the $3$ results is $\dfrac {8+11+4}{3} = 7. \overline {6}$

• Before explaining a phenomenon, we have to describe it accurately. Can you provide any evidence that this person really can influence your choice? I couldn't do it myself because I read your summary first, but I'd be surprised if the video made any difference. It may also be worth noting that people do not behave randomly when choosing numbers and 7 is a popular one anyway (it's many people's lucky number, for example). – splint Aug 4 '16 at 12:09