> owning real estate that someone else manages or really owning any business that someone else fully manages for you
If you've ever owned real estate or a business you'd know it can't be 100% passive. Even with a property manager, there are always things to fix, change, or update, and the associated decisions to make about it. One bad tenant or a property manager with bad judgement, and you're 100% back in full-time landlord mode to clean up the mess (literally or figuratively).
you can in fact pay agencies to deal with ALL of that, they just take it out of your cut. have you owned real estate or a business? I have both and i can attest they can be fully managed by others, without headache to the owner, its very simple. industrial RE investors do this all the time.
I do in fact own both, and they only run on whir own until your agent screws something up. It may require less work than other forms of income, but if you expect it to work out long term, it can never be completely passive.