Unexplained features of our brain

Dear Habravchani, your attention is a small task that will prove to everyone once again that the mystery of the human brain is far from being solved.

At your disposal you have 10 seconds, otherwise it will not work.
All you have to do is count the number of letters "F" in the text below.
Remember, no more than 10 seconds!

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FINISHED FILES ARE THE RE-
SULT OF YEARS OF SCIENTIF-
IC STUDY COMBINED WITH THE
EXPERIENCE OF YEARS
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Explanations under the cut

How much did you get? Three letters?
Not properly! There are six of them !
This is not a joke.

It turns out our brain is not able to recognize the preposition "OF".
Those who managed to recognize 6 letters can consider themselves a genius.
Those who identified 4 or 5 letters are quite rare.
People identified 3 letters are absolutely normal.
Those who did not recognize and the two time to change points.

PS I recognized 4 letters, but when I decided to check myself I counted three. ))