The connective tissue across the other pillars: discovery through implementation to a clean handoff, or a transition into ongoing support, run as one coherent engagement.
Bigger engagements often touch more than one pillar at once: an infrastructure review that leads to a migration, followed by a CRM implementation, followed by ongoing support. Treating those as separate projects usually means duplicated discovery and inconsistent decisions along the way.
This mirrors the Technical Account Manager lifecycle Khal ran at VMware: discovery, implementation, and steady-state management as phases of one relationship, compressed here into a project format instead of a standing enterprise account.
This pillar describes how larger, multi-part engagements get run end to end.
If your project touches more than one of these pillars, that's exactly what this one is for.
Bring the messy version. Scoping is where it gets untangled.