It is no use throwing good money after bad.

Understand the thought

Meaning in plain English

Do not keep adding resources to a failing course merely because you have already spent some. Judge the next commitment by what it can achieve now, rather than by a wish to justify the past.

What the words are saying

Good money represents resources still available; bad money is what has already been spent without a worthwhile result. The image warns against extending a loss simply to avoid admitting that an earlier choice disappointed. It can apply beyond spending, including time spent on an unsuitable plan. The saying does not establish that every struggling project should stop. New information or a credible change may justify continuing. Its useful question is whether the next contribution has a reasonable purpose of its own, instead of being driven only by attachment to what can no longer be recovered.

Everyday example

A group stops buying decorations for an event after the venue cancels, checking what can be reused before committing more to the original plan.

When to use it

Use it when a further commitment is being justified mainly by what has already been spent.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.