Supplementary Material .01 states the general principle: fair dealing with customers and others is implicit in every member relationship, so selling must stay inside the ethical standards FINRA's rules set, above all the obligation of fairness towards the investing public. Suitability is the concrete expression of that obligation; it exists to promote ethical selling and a high standard of professional conduct. Compensation, incentive and sales-contest design is the usual test of whether a firm honours it.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.