In striving to achieve the desired per-share number, a panting CEO and his “helpers” will often conjure up fanciful “synergies.” (As a director of 19 companies over the years, I’ve never heard “dis-synergies” mentioned, though I’ve witnessed plenty of these once deals have closed.) Post mortems of acquisitions, in which reality is honestly compared to the original projections, are rare in American boardrooms. They should instead be standard practice.

