In the absence of evidence, superstition. It's a Middle Ages thing. That's my theory anyway.

We forget how bawdy and brutal the Middle Ages were.

It flourished with the Saracens, and suffered in the obscure and fanatical days of the Middle Ages.

There is something dark and wintry about the atmosphere of the later Middle Ages.

I was nuts for stuff in the Middle Ages when I was just in the third and fourth grades.

Two of the most famous Baghdadi scholars, the philosopher Al-Kindi and the mathematician Al-Khawarizmi, were certainly the most influential in transmitting Hindu numerals to the Muslim world. Both wrote books on the subject during al-Ma'mun's reign, and it was their work that was translated into Latin and transmitted to the West, thus introducing Europeans to the decimal system, which was known in the Middle Ages only as Arabic numerals. But it would be many centuries before it was widely accepted in Europe. One reason for this was sociological: decimal numbers were considered for a long time as symbols of the evil Muslim foe.