Nihil admirari (or “Nil admirari”) is a Latin phrase. It means “to be surprised by nothing,” or in the imperative, "Let nothing astonish you."
Marcus Tullius Cicero argues that real sapience consists of preparing oneself for all possible incidents and not being surprised by anything, using as an example Anaxagoras, who, when informed about the death of his son, said, “Sciebam me genuisse mortalem.” (I knew that I begot a mortal).  Horace and Seneca refer to similar occurrences and admired such moral fortitude.  
'Marvel at nothing'--that is perhaps the one and only thing that can make a man happy and keep him so.