to do something that is dangerous or only just legal or acceptable
就是字面意思来的：
based on the literal meaning of sail close to the wind (to sail a boat as near as possible to the direction the wind is coming from)
最初用于航海
Taken from nautical terminology:if a boat under sail heads directly into the wind it will be stopped by the backward pressure of the sails against the masts.Sailing ‘close to’ the direction from which the wind is blowing is therefore risky but makes for more rapid progress than sailing at a more oblique angle.