The reason for it is because it doesn't work 100% of the time, but don't let that put you off.
I personally have a 90% strike rate and it's so simple to perform you can perform it today.
You can perform it any time, anywhere to freak people out and show them you have special abilities.
What you do, is you say to someone, "Think of a colour", you then say..
"Hmmm, You changed your mind a little there, I wanted you to think of the first colour, the first colour you thought of was red..
" Pause for a moment to gauge their reaction and say..
"then unconsciously you changed to blue
What colour did you choose in the end?" Nine times out of ten they will be shocked as soon as you mention red and you won't have to say the line about blue and purple so you will have your miracle straight away, sometimes they will shake their head or not react after you say they thought of red which then means you need to deliver the blue and purple lines.
That's why you need to pause for a moment to see their reaction first.
This trick works on the basis from studies whereby they asked a load of people to think of a colour and red was the most common, followed by blue and then purple.
Also, some people will think of red and then change to blue as well.
All you have to point out that they could have unconsciously changed the colour so you're covered.
Of course I only do this trick if I know I have a few other tricks I can perform after this trick because if you get it wrong, you want them to forget about it while you perform another trick.
I personally use this trick as a 'test' to see if they will be good candidates for my mind reading tricks.
It's not a real test, but I tell them it is so if I get it wrong, I was only 'testing them'.
Testing THEM, not ME.
Don't underestimate this baby, it's really powerful when it hits and can set you up to use your ultimate mind reading tricks to REALLY freak people out.