Learning how to do the work, when you already is on the job is rather common, but not always recommended as two sailors found out a while ago.
The question is how to learn how to do the work on the job, while keeping the expectations on the right level. Especially if you are the only person in this role, you haven’t done it before and there are no methods or instructions to learn from. You more or less have a mission impossible situation if the expectations are to deliver full, or near full performance from day one.
How can we mitigate these situations in before they happen?
With a certification, the person at least has a basic knowledge of what to do, compared to a person without any formal training. If you do ocean sailing, at least get a basic sailing course before leaving the harbour. Don’t do scuba diving on your own without a dive certificate.
As a project manager, be familiar with at least one project management meted. As a business analyst, learn methods and business that are relevant for your assignment before you start. As an Enterprise Architect, learn a method and how to apply the framework in real life.
The best way to mitigate the risks is to be part of a team, so that you don’t have the full responsibility as a rookie, even if you learned the basics before. If you don’t have this possibility, at least have an experienced colleague to call when, not if, something goes wrong.
Navigare necesse est