The failure is not technical
Ask a room of executives about a failed ERP programme and you will hear about scope, timeline and vendor performance. Ask the people who use the system and you hear something narrower: the process it enforces is not the process the work requires.
Technical failure is rare and visible. Operational failure is common and quiet. The system runs, the reports generate, and the operation goes around it.
Day 91
Most implementation contracts end at hypercare. That is roughly day 90. The behaviours that decide whether the investment returns anything form on day 91 and in the ninety days after it — when the project team has gone and the operation decides, without supervision, whether the new process is worth the effort.
If nobody owns adoption at that point, the operation reverts. Not dramatically; incrementally, through workarounds that are individually reasonable.
What to do instead
Write the operating metric into the contract. Sequence the organisational decisions before the configuration decisions. Give adoption an owner whose own metric depends on it. And plan the ninety days after the project team leaves with the same seriousness as the ninety before go-live.