As a physicist working as a software engineer at a hardware company, I can give a bit of an explanation for this: 1. Doesn't matter if you're in the business o

As a physicist working as a software engineer at a hardware company, I can give a bit of an explanation for this: 1. Doesn't matter if you're in the business of widgets or SaaS or whatever. Business is business. 2. There are really only two engineering disciplines you need a strong intuitive understanding of: systems and physics. It is completely possible to be very skillful at all three of these. However, even for Elon Musk, it would still likely take months of training to keep up working in a new engineering discipline including all of the idiosyncrasies and tools. There are plenty of people who are highly knowledgeable in 5+ subjects, but virtually none who are capable of working as a diverse, skilled experts in more than 3. If you want to be an expert in multiple fields, find underlying 'core' disciplines and become an expert on those.