What defines loyalty? U.S.A. companies search for the holy grail of brand loyalty in consumers to harvest a lifetime of purchases. So I began thinking about what companies or products have I been loyal to for over twenty years (since 1996). Sony, Cincinnati Bell, General Motors, Yahoo, Sams Club, Kroger, Allen Edmonds, Microsoft, Amazon, PNC Bank, Schwab, Verizon, Vanguard, Delta Air, Hertz, Marvel, Duke Energy, Accenture and a few food brands.
Some of what defines loyalty is "first to market" as is the case with my bank, brokerage, and wireless provider. Those relationships are "sticky" and requires effort to change. Others becomes convenience (location/monopoly related), Microsoft, Kroger, Delta Air, etc.
There have been some loyalty tests for many in my list, but each company was able to survive the temporary dissatisfaction with appropriate customer service.
Loyalty in human relationships (see "Earn a Friend"), or in groups (clubs, ideologies, religion, nationalism etc.) is quite different and not necessarily exclusionary. Sometimes loyalty is misplaced as duty and recklessly followed to one's demise.
Loyalty is best described as commitment. Commitment requires passion. Sustainable passion means willing to forgive. Loyalty takes time and tests but yields a lifetime of rewards.