Does anyone know?

I used to know how this works, but can't remember. Can anyone tell me?

http://milaadesign.com/wizardy.html

 

got me once, not the 2nd time.

50%

 

It's gotten me every time...even when I tried to fool it!

 

If you'll look carefully, the same pattern of symbols is repeated over and over again. Odds are in it's favor.