“a hair’s breadth”别理解成“一根头发的宽度”，其正确的含义是极短的距离；毫厘之差；细微的量。

【例句】
The seal is air-tight—there's not a hair's breadth between the door and the frame.
封口是密不透风的，门和门框之间没有毫厘之差。

We won by a hair's breadth.
我们以些微之差赢了对手。