The Sankey diagram is visually highlighting the areas of biggest consumption, impact, cost or risk. Naturally what is thickest has more relevance and is therefore most interesting.
Exercise: Drill into the Ball tip model starting from the Ball Pen Mattermaps.
Step 1: Mark the product you want to drill into by clicking it with the left mouse button. (number 1.) In our case it is the ballpoint tip.
Step 2: You can control that what you selected in the info and tool panel (see number 2.) The name shown should be "Ballpoint tip"
Step 3: Now click on View product model (marked with 3.) and the lower tier model will open.