It is never too late to mend.亡羊补牢
Once upon a time, there was a shepherd who kept several sheep.
One morning, the shepherd discovered that one of his sheep was missing.It turned out that, during the night, a wolf had stolen his sheep through a hole in the sheep pen.
His neighbor suggested to him: "You should fix the pen and cover the hole right away."
But the shepherd said: "The sheep is already lost, so I don't need to repair it." And so he rejected the neighbor's suggestion.
The next morning, he discovered that another sheep was missing.Once again, the wolf stole the sheep through the hole in the fence.
The shepherd regretted not taking the neighbor's advice.So he plugged the hole to secure the sheep pen.
From then on, no more sheep was stolen by the wolf.
英语中如果想表达同样的意思，我们可以说“It is never too late to mend.”，也就是“补救永远不嫌太晚”。