To illustrate how modern superstitions can affect our daily lives, take the word "adolescence". Every "rational" person in the contemporary society agrees that there is a stage called "adolescence" in human life. But see the fact here (copied from a web archive on sexology):

"Adolescence: The period between the beginning of puberty and adulthood.
The phenomenon of adolescence as we know it today is the result of certain social and historical developments. "Pre-civilized" cultures do not know an adolescence in the modern sense of the word, but use so-called puberty or initiation rites by which they confer the status of adults on their children as soon as these have reached a certain age (usually between 12 and 14 years). This means that, in these cultures, the period of transition from childhood to adulthood is very short. The same was true for our own culture in ancient times. The traditional customs from that period live on in contemporary religious ceremonies, such as the bar mitzwah and the Catholic and Protestant confirmations. However, with the development and growing complexity of civilization, the transitional period between puberty and adulthood has gradually become longer until, as in many contemporary societies, it now extends well over 10 years and more. It is not impossible that, in the future, the period of adolescence will last even longer. As is obvious from this short sketch, adolescence is less a biological than a cultural phenomenon."

If you don't mind, the link for the above is:
http://www2.hu-berlin.de/sexology/GESUND/ARCHIV/CDS.HTM