If we define failure as the inability to meet pre-merger/acquisition KPIs once post-merger activities have concluded, then I have seen moderate failure. Post merger activities have been monitored closely, but a lack of priority beyond the commercial success of the acquisition has caused delays and increased costs in terms of time and priorities. I have found. so far, that due diligence is often limited in scope, pre-merger forecasts are often tied to closely to assumptions and estimations with little cross-functional input, and post-merger designs are poorly actioned. The last of these often causes the most trouble. Delays in ERP integration, product documentation or history, and user training and functionality round out some of the gaps in a successful merger in my experience.