this is indeed one of the fundamental things that you need to learn in order to rigorously disaggregate the value drivers of a business. The driver tree allows you to identify the numerical drivers and sub-drivers of profits. The qualitative elements (such as consumer demand, market structure, company operations, etc.) then have to be mapped to the sub-branches of the tree!
Hence, your analysis has two steps. Imagine you want to run a diagnostic on why profits have fallen. First you need to identify the numerical driver of the problem (e.g., customer base is shrinking). This gives you an understanding of the WHAT. The second step is the understanding of the WHY! To do this, you have to examine the qualitative elements that link to the "number of customers"-sub-branch in your driver tree (e.g., competitive situation, market entries, new substitutes, relative price point, customer preferences, product/service properties vs. competition, etc.)
You can think of these qualitative elements as the typical business situation framework elements (see V. Cheng et al.) - but here, they are not hanging in the air, but they are embedded in a rigorous thinking frame which emerges from the disaggregation of value drivers and linking it to qualitative reasons.
Dr. Sidi Koné
(Former Senior Engagement Manager and Interviewer at McKinsey | Former Senior Consultant and Interviewer at BCG)