Yeah, that’s exactly the tricky part — most failures come from planning and execution, not technology. A lot of companies underestimate how much critical logic is buried inside legacy code. If a vendor doesn’t properly analyze and preserve it, you can end up with a “modern” system that actually breaks real workflows.
Also, the whole “big bang rewrite” idea sounds nice, but in practice it’s super risky. Most experienced teams recommend phased modernization, where parts of the system are upgraded gradually while everything keeps running.