The management guru Tom Peters once said, “Excellent firms don’t believe in excellence—only in constant improvement and constant change.”

When he said that—perhaps while walking around—he must have been channeling the Greek pre-Socratic philosopher Heraclitis, who said, “The only thing that is constant is change.” (Heraclitis is also credited with saying, “One cannot step into the same stream twice,” which seems to be effectively the same thought.)