You must lose a fly to catch a trout.

The proverb uses an angling image to express a general principle of exchange: to gain something larger or more valuable, you must be willing to spend or risk something smaller. “Lose a fly” evokes sacrificing bait—something expendable—to “catch a trout,” the desired prize. In moral and practical terms, it points to calculated investment, opportunity cost, and the necessity of giving up immediate, minor goods (money, comfort, pride, time) to secure greater ends. It can also imply strategic patience: the apparent loss is not waste but a means to a worthwhile outcome.