Onboarding is usually evaluated by how the new employee feels in week one. The more consequential cost sits elsewhere: in the repeated interruption of the experienced staff who become the de facto knowledge system.
When information is not retrievable, the organization defaults to asking a person. Every one of those questions has a price paid twice — once by the new employee waiting, once by the expert who stops what they were doing. Neither cost appears in any onboarding budget.
The second hidden cost is variance. When the experience depends on start date, team, and supervisor availability, two people hired the same month can develop meaningfully different working practices. That variance surfaces later as inconsistency, and gets misdiagnosed as a training problem.
The remedy is not a better orientation week. It is deciding deliberately what genuinely requires a human — judgment, relationship, context — and building structured, findable support for everything that does not.