These are the lessons from the selling side. From the buying side there's a different set of lessons, like: they sold us junk that doesn't really work, their people are leaving to another start-up the founder created, nightmarish regulatory violations that only pop up after the merger, having to re-build their entire tech stack/accounts from scratch because it was all built by hand and held together with masking tape, contracts not discovered until after the merger, vetting all software licenses and use cases, the product not being able to integrate with your product like they claimed, 10 years of tech debt. Then there's how much time and money you lose and risk you gain from not doing enough due diligence or not having an efficient onboarding/integration process. I've been at large companies that were M&A masters, and companies that have done dozens of M&As and still can't get a single one right.