The application layer
Enterprises keep buying technology and stacking it on what already runs. The failures show up between people, vendors, SI teams, and siloed data.
Everyone owns their piece. Vendors own the product map. SIs own the delivery map for their mandate. The company rarely owns the operating map above them. Systems, six process constellations, and people on a company-owned data core. I have spent 30 years doing exactly that: keeping the operation up while the stack moves.