It's in the "shades of gray" where subjectivity rules and auditors get lost.
Subjectivity can lead to "opinions" and that's when an audit can become a blasting success or too often a (miserable) failure..
Either we like it or not, life, business, auditing, etc. is, for the most part, full of variables and sprinkled with a few attributes here and there. People who try to live their lives via a checklist mentality with yes/no boxes have a hard time coping with reality.
When it comes to management system auditing, the vast majority of situations auditors are confronted with is a "degree of conformance". Auditing requires the ability to judge complex situations. While criteria is always necessary to guide our work, all attempts to develop all encompassing and prescriptive rules and criteria that, designed to cover all possible scenarios, are destined to fail.
That is exactly why we have documents such as ISO 19011, which provides guidance on how management system auditors should perform. That is why auditors need to be COMPETENT. They need to assess the situations within the context and risks involved.
Let me offer a simple scenario. Most people would say that a single instance of an obsolete document identified, out of 235 documents checked, during an audit, would lead to a either a non-consequential "observation" or minor non-conformity, isn't it? The problem is not systemic, would most people argue.
Well, what if the single piece of obsolete document observed during the audit is the FINAL INSPECTION AND TEST criteria? And, from the previous revision to the current, the actual accept/reject numbers have changed. In other words, we could be accepting defective products by using this obsolete specification, which would bring risks from the customers perspective, or we could be rejecting perfectly good products, which would be detrimental to the organization's bottom line.
Either way, one single piece of outdated document can have dire implications. So, would you categorize that situation as an observation, minor or major NC?
Real auditing is not easy. It does require a lot of things, such as analytical skills. Because subjectivity abounds everywhere we go. And we have to deal with it.