Except you make your living of it. I'm an amateur. You must obey the customer. I'm my own and only customer, which is a very comfortable situation because I can always achieve the golden middle between effort and expenses I'm going to spend on the project and expectations about the result. For me, "just works, mostly" often happens to be perfectly satisfactory quality, and I can freely stretch specs, violate regulations, abuse features, and I don't risk my reputation or failure in unknown conditions. You are bound by a lot of regulations, you can't afford the devices to work at the border of their capablities and beyond range defined in specs, you can't afford savings on "ugly hacks" like using duch tape and chewing gum to keep things together. And I can enjoy sharing my ideas and designs with others, you need to keep them secret. It's just that you get money from that, and I only spend them.