Essentially that using the graph DB prevented any imposition of order or discipline on the structure of the data, due to the constant need to import new customer data in subtly different structures to keep the business running, which led to a complete inability to deliver anything new at all since no one could make assertions about what's in there. Since they couldn't change it without risking breaking a customer they were migrating one customer at a time to a classic RDBMS. (There were like 200 customers, each of which is a company you've probably heard of).
Many will go "you need a proper ontology" at which point just use a RDBMS. Ontologies are an absolute tarpit, as the semantic web showed. The graph illusion is similar to that academic delusion "It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures." which is one of those quips that makes you appreciate just how theoretical some theoreticians really are.
Many will go "you need a proper ontology" at which point just use a RDBMS. Ontologies are an absolute tarpit, as the semantic web showed. The graph illusion is similar to that academic delusion "It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures." which is one of those quips that makes you appreciate just how theoretical some theoreticians really are.