Add-on acquisitions are a genuinely good strategy, which is exactly why they’re so easy to get wrong. 

The logic is sound often enough that people stop interrogating it case by case, and that’s when the bad ones slip through. 

The pattern I keep seeing: a bolt-on gets pitched on revenue synergy that assumes cross-sell will happen roughly the way it does on the slide. 

Combined customer base, combined product suite, obvious upsell opportunity. What the slide doesn’t model is that cross-sell motion has to be built, not assumed, and building it usually requires sales team retraining, product integration work, and often a repricing exercise, none of which show up as a cost in the original deal model because they weren’t really costed, they were assumed away. 

Eighteen months later, the acquired business is still operating largely as a separate unit, the cross-sell numbers never materialised because nobody actually built the motion, and the combined entity is now carrying two sets of overhead for the revenue benefit of one. This isn’t a failure of the underlying logic, it’s a failure to plan for the fact that synergy is a project, not a consequence. 

The question worth asking before any add-on gets approved, and the one that gets skipped most often under deal timeline pressure: who specifically owns building the cross-sell motion, what does month one of that actually look like operationally, and what does the model assume happens for free that will actually require dedicated headcount and time.

If nobody can answer that with specifics, the synergy case is a hope, not a plan, and hopes are exactly the thing that look great in the deck and evaporate by year two.