cross a bridge when one comes to it

Idioms  

1. Also, cross that bridge when you come to it. Deal with a situation when, and not before, it occurs. For example, If we can't sell the house—well, we'll cross that bridge when we come to it. The ultimate origin of this proverb, a caution not to anticipate trouble and often put as don't cross a bridge till you come to it, has been lost. The earliest recorded use is in Henry Wadsworth Longfellow's The Golden Legend (1851): “Don't cross the bridge till you come to it, is a proverb old and of excellent wit.”

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