Take advantage of an opportunity while conditions are favorable, act quickly when the moment is right.
Originates from blacksmithing, where iron must be shaped while it's heated and malleable. The phrase appears in English literature as early as the 16th century, with similar expressions in many languages reflecting the universal nature of metalworking.
This is one of the few idioms where the literal and figurative meanings are perfectly aligned - blacksmiths literally cannot work cold iron! It's a beautiful example of how manual trades gave us timeless wisdom about timing and opportunity.
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