also: ぬすびとにおいせん
throwing good money after bad
Idiomatic expression meaning to waste more resources on something already lost or failed, like giving more money to a thief who has already stolen from you.
Investing more in a failed business is what they call throwing good money after bad.
Both describe futile efforts, but 焼け石に水 emphasizes an insufficient measure (like a drop on a hot stone), while 盗人に追い銭 focuses on compounding a loss by adding more resources.
Standard kanji form for the idiom; 盗人 is read ぬすっと here.
Alternate reading of 盗人 as ぬすびと; less common in this idiom but recognized.
The literal meaning is 'giving additional money to a thief.' It figuratively expresses the idea of wasting more resources on something already lost. The exact origin is uncertain, but it is a traditional Japanese proverb.