Within two years after becoming chief executive of General Electric in 1981, Jack Welch completed one of his most far-reaching initiatives: reducing the number of GE business units from about 150 to 15. In effect, Welch set out to focus the company on the businesses where it had the potential for greatness, and to jettison everything else. That was the point of his famous requirement that every business had to be No. 1 or No. 2 in its market; he also insisted that every business provide value no competitor could match, and that they all should be able to gain leverage from GE’s distinctive strength in complex, engineering-intensive industrial enterprises — or they wouldn’t fit. Welch articulated both what GE did well, and what it would not do at all: a critical challenge for all large companies, especially conglomerates.