Should we fix this bug or not? Four questions to ask!

In My life as a Code Economist Eric Sink tells you about a terrible week he had at SourceGear, releasing three “maintenance-releases” in one week.
He argues on the “Should we fix this bug or not” stating four questions:
 
Question One
When this bug happens, how bad is the impact?
Severity
Question Two
How often does this bug happen?
Frequency
Question Three
How much effort would be required to fix this bug?
Cost
Question Four
What is the risk of fixing this bug?
Risk
 
Eric gives some great annotated examples of stating these questions on some actual items on his buglist.