You do, but not all such assets are expensive (in money - most cost a significant investment of time up front to create). Intellectual property (apps, writing, music) is a popular one. A more concrete example with relatively low capital investment (say, within the reach of someone with a 5-figure income) might be a rural highway billboard, or a snow-blower that you rent to your neighbors after storms. I remember reading a story about someone who built a miniature vending machine empire.

Often, extracting rent from such an asset takes some small amount of ongoing work (ex: marketing; app maintenance; pasting new ads onto the billboard; refilling the vending machine every couple weeks), but such work is either relatively infrequent or scales your income much better than being paid directly for your time does.

Royalties from a book or patent or software?