[greenyoda]

The problem with logs is that programmers log the data that they believed, at the time they wrote the code, would be useful to help diagnose problems. However, many bugs arise from conditions that programmers failed to anticipate, and thus may have failed to log.

Also, there are important things that you just can't log for legal or ethical reasons. For example, no user of a browser would be happy to know that the current URL they were viewing or their POST data was sent back to a browser developer (or even saved in a local file) without their explicit permission.