It appears to come from a book called The Open Door (http://www.quotationspage.com/quote/30188.html)
But is it a useful maxim for life? It seems not, to me. One can realize that true security is a myth, but that doesn’t suggest that one should seek out danger for the sake of seeking out danger. Neither should one avoid any danger at any cost and thus fail to do and learn. This maxim, while food for thought is just as useful as, “love thy enemies, do good to those who misuse you,” which has truth behind it, but taken literally, is absurd.