Why is it more costly to discover a defect later in the process?

agile, debugging

Solution

The longer it takes to find a bug, then:

the more the behavior of the bug may have been accepted as correct, and the more other things may have become dependent on that behavior (Windows is notorious for this).

the more tightly integrated the system is likely to have become, and the harder the bug will be to extract.

the higher the likelihood that the bug's erroneous behavior will be duplicated elsewhere by virtue of copy-pasting or in clients that use the erroneous code.

the longer it's been since the code was originally written and the harder it may be to understand it.

the less likely it will be for people who understand that original part of the system to be around to fix it.

Problem

Original source