don't shut the stable door after the horse has bolted

The phrase "don't shut the stable door after the horse has bolted" is an idiom used to convey the idea that taking action or implementing preventive measures after an event has already occurred is futile and ineffective. It implies that one should take necessary precautions or preventive steps beforehand to avoid undesirable consequences rather than trying to fix things after the damage has been done. The phrase suggests that it is important to be proactive and address issues before they escalate, rather than reacting too late.