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general::
Phrase(s): Keep a thing seven years and you’ll (always) find a use for it.
Prov. If you keep a seemingly useless thing for seven years, you will supposedly have some occasion to use it during that time. • Jill: My mother sent me a four-foot-tall ceramic vase for my birthday. What can I possibly use it for? Jane: Keep it seven years and you’ll find some use for it.
McGrawhill's American Idioms And Phrasal Verbs