MDM rarely fails on platform capability.
It fails on four decisions taken early, quietly, and usually by whoever happened to be configuring the tool that week. Each one is cheap to get right at the start and expensive to unwind later.
The golden record was defined by the source, not the consumer
The model grew outward from whichever system loaded first. Nobody asked which decisions the record has to support, so survivorship was configured for every attribute equally.
Trust hierarchy was set as a technical parameter
Trust scores encode a commercial judgement about which system is authoritative. Configured without that agreement, they get disputed the moment a business owner sees their system lose.
Match rules shipped on vendor defaults
Defaults are a starting point, not a configuration. Without precision and recall measured against a labelled sample, you have opinions about match quality rather than evidence.
Stewardship was sized to the configuration
If the platform generates more tasks than the team can clear, the backlog grows indefinitely — and to everyone downstream an unworked backlog is indistinguishable from bad data.