Read this sentence:

FINISHED FILES ARE THE RESULT OF YEARS
OF SCIENTIFIC STUDY COMBINED WITH THE
EXPERIENCE OF YEARS.

Now count the F's is that sentence. Count them ONLY ONCE.
Do not go back and count them again. Then see below:

There are 6 F's in the sentence. One of average intelligence finds 3 of them. If you spotted 4, you're above average. To see 5 is rare. If you caught 6, you are a genius. There is no catch. Most people forget the OFs. The human brain tends to see them as Vs instead of F's.

So... How smart are you??

(мозг часто пропускает слово OF)