every flow must have its ebb

proverb All periods of good fortune are followed eventually by periods of ill fortune, and vice versa. ("Ebb" and "flow" are typically used in reference to the tide: "flow" for the rising of the tide and "ebb" for its receding.) I try not to get overly excited when things are going well because I know that every flow must have its ebb—that's just how the universe works. Any businessperson worth their salt knows that every flow must have its ebb, so they should try to save money prudently during periods of success.