live by/on one's wits
混日子
A:Do you know that Jack got divorced last month?
A：你知道吗，杰克上个月离婚了。
B:For what reason?
B：为什么?
A:Jack always lives by his wits and he cannot support his family.
A：他一直靠耍小聪明混日子，根本不能养活自己的家庭。
B:He'd better make a change.
B：他是应该改改了。