Depends? If it was from the ground up then hiring the right people would probably be the first challenge. Past that is managing them. As a business owner I'd always reckon you only need a few things to do. To point the direction where the company should go and to manage the people under you to keep the business running. Not really your job to know how to do X or how to do Y, that's why you hired personnel in the first place! Ofc this also includes taking responsibility and possible actions/measures when ventures are a failure.