What is a Methodology?
A methodology is a defined system of practices, techniques, procedures, and rules for running projects — PRINCE2, SAFe, a company's in-house stage-gate manual. The PMBOK Guide, by its own insistence, is not one: it describes what good project management addresses; a methodology prescribes how, step by step.
The healthy relationship is methodology + tailoring: the manual provides consistency and shared vocabulary, and professional judgment cuts it to fit each project's size and risk.
Worked example
An engineering firm's methodology mandates five gates, standard templates, and monthly EV reporting. For a $50M plant upgrade, all of it earns its cost. For a $60K pump replacement, the tailoring guide inside the same methodology says: two gates, one-page charter, no EV. Same system, both times — that's a methodology working as designed, not being ignored.