It is one thing to innovate and achieve breakthrough success—to reach the pinnacle, the mountain top. It is quite another to sustain that leadership position decade after decade, in a competitive marketplace that has become increasingly digital and data-and-analytics driven. The ability of American Express (AMEX) to sustain its brand and continue to reinvent and build upon its core strengths as a leader in customer experience and payment processing is a rare and notable feat. Founded in…