For example... someone who is a computer engineer and his expertise is machine vision or voice recognition or totally machine learning (ML) fields. But we know a robot has electrical parts and mechanical parts as well. Also, it's possible to consider we might like to create an application on Web/Windows/Mac/Android/ios for our robot too! And many other possible extra conditions.
So, our founder/project manager is a great man in the ML field but not in web/mobile/electronics/mechanics and other fields of engineering that may needed for the company. Then, how should he manage people with other areas of expertise and evaluate if they are the best people to choose and hire? To do they their jobs well (I mean, there is no better/easier/less expensive way to do that job)? And when one of them is stuck in his/her job and couldn't find the solution, how can he help him/her to get the job done?