"Anything you don't understand is dangerous until you do understand it."[2]
Simple: Things appear dangerous until you understand them.
References
↑As quoted in Reader's Digest Quotable Quotes : Wit and Wisdom for All Occasions from America's Most Popular Magazine (1997) by Reader's Digest Association, p. 27
↑"Flatlander" (1967), first published in If (March 1967)