That's the right question. I don't like this dichotomy between domain and engineering. It seems to come from people who just build different CRUD apps for mobile and websites for businesses in different industries and that's what they call domain.
Not like a webdev entering game engine design or a database engineer entering computer vision research, or someone working in embedded hard-realtime systems switching to making video editing GUIs.
That's a fair question. I suspect highly specialised industries are harder (rocket and space, defense, nuclear, etc), but for things like finance (most of it, anyway) and retail, which IME make the bulk of the tech jobs out there, it's certainly nothing out of this world.
I suspect you're a junior engineer if you think that way. Domains (any) are deep, and require thorough understanding before you can have business or revenue impact.
I do feel like a junior engineer sometimes. Funnily I didn't as much for the first 15 years or so, but the longer I go and the more clients I work in, the more I feel like it - and I find it refreshing!
I agree that domains are deep but rarely I'll touch all areas of the domain in any given role. As I mentioned in other comments, I don't have to know all of it, as there are other people in the business and likely within my team who:
- probably don't know 100% either; but
- know things that I don't
We work together so as a team we have as broad and deep a domain knowledge we can for the needs of our products and projects.
Not like a webdev entering game engine design or a database engineer entering computer vision research, or someone working in embedded hard-realtime systems switching to making video editing GUIs.