If you start simple and follow cookbook and "handbook" designs and have a passion for learning how to improve a design, then understanding all the component non-ideal characteristics of passive and active parts is essential. If you prefer the logic of Finite State Machines or programmable logic and uC, there is a wealth of complex logical designs to make simple cheap solutions.
I have enjoyed many different facets of design from designing radios, UARTs, SCADA controllers, telecom T1 test sets, HDD test equipment, world's smallest TV monitor etc etc from the 70's thru to 2002 then designed for other companies on contract. It is best to learn by reverse-engineering proven designs, then learn the process. A keen eye for hidden features to make it reliable, realizable and cost-effective, quickly with high customer-satisfaction are almost impossible to say in the same sentence. These trade-offs are what makes it interesting for me.
But if you want to get rich, get experience then become self-employed, if you can afford the tools.