The ten-year figure is the one to sit with. A deal can look successful for years, clear every integration milestone, survive the period any conventional study would measure, and still be unwound long after the people who did it have moved on. That is a different and more sobering picture of risk than the announcement-return literature can give you, and it is why the Institute keeps asking what you intend to do with the business rather than what you intend to pay for it.
The authors identify two distinct causes, and they fail on different clocks. The first is poor initial fit, whether strategic misalignment or cultural mismatch, which is present at signing and merely takes years to surface. The second is unforeseen disruption arriving well after closing, which no amount of diligence could have caught. Only the first is yours to prevent, and it is the one diligence and honest self-assessment actually address.
The consolation, such as it is, is bounded: roughly half of divested deals do not add shareholder value, meaning selling the mistake is not reliably a remedy either. The authors also note what a failed merger costs beyond money, absorbing leadership attention, damaging credibility and eroding morale, which for a private company with one management team is the whole company rather than one division of it.
Read directly against the Bain research also added here, which finds close to seventy percent of deals now succeeding. The two are not measuring the same thing: Bain asks whether a deal met its objectives, this asks whether the business was still owned a decade later, and a company can answer yes to the first and no to the second. Holding both is the honest position.