READ this sentence:
FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS.
Now count aloud the F's in that sentence. Count them ONLY ONCE; do not go back and count them again.
There are six F's in the sentence. One of average intelligence finds three of them. If you spotted four, you're above average. If you got five, you can turn your nose at most anybody. If you caught six, you are a genius. There is no catch.
There is also a tendency for us to block out the so called unimportant words, in this case OF...