That's easy. Lies, misdirection, and the person doing the technical due diligence being a C-Level/Director with zero IT background but plenty of project management experience.

They know just enough to be dangerous and frustratingly useless getting useful information from. So your integration team has to do all the planning with only the foggiest idea of what they are getting into. They then spend the entire first day on the ground just getting the lay of the land. No time to schedule local cable contractors for the really needed cable runs. Let's hope that the existing CAT5 runs work fine on gigabit for the next few weeks till we can get those contractors in to replace all the wiring. Worse case, we'll have to limit the port speeds to 100Mbps at the new switch if retransmits become an issue.

Even more fun when the next project is even less detail but the entity you are acquiring is on another continent instead of a few states over.

Reminds me of HP's 11.1 Billion dollar blunder of buying Autonomy....

https://www.nytimes.com/2012/12/01/business/hps-autonomy-blu...

Sturgeon's revelation: 90% of everything is crap applies to due diligence.

I just remember two of our engineers had a gig, spent 6 months at $150/hr wading through VHDL and C++ code of some company that was being acquired. They also had to work closely with a patent attorney who was billing probably $500/hr.

Have been there for an acquisition that did not go as planned. Essentially on the small side you are very dependent on the disclosure of the parties involved; short of truly burdensome diligence processes you are sure to miss things if the company being acquired is not up front about things.