It isn't hard to infer. This is about confounding effects of non-professional tangibles. Human judgement is often influenced by non-technical qualities.

eg You'll find that the advantages offered by being attractive is tangible, but never quantified. It can allow you more stable employment, as unfair as that may seem in the abstract.

This is a little off-the-path, but is additive. Domain experts, for example, often get a lot of leeway in performance reviews because it isn't always needed. If you're hired on as a DB2 expert, you're golden because DB2 is a sub-standard database and you get to answer questions in the most forgiving manner while doing almost nothing - "it doesn't do that" "that's not available" "there is no standard practice".