I know a dentist who opened a brand new clinic without a single patient.

No referrals. No reputation. Nothing.
Right across from his practice were two apartment complexes:
600 units in one and 400 in the other.
He went to the rental offices of both buildings and introduced himself.
Everyone who worked there became his free patients.
Free cleanings. Free whitening.
He did it on purpose.
The rental office employees talk to every new person who moves in.
Without realizing it, they became his referral network.
Every new resident received a toothbrush, toothpaste, and a handwritten card from him.
He also went door to door in both buildings.
He carried a spreadsheet with every door he knocked on.
Twelve months later he has 350 Google reviews, almost all from those two complexes.
He's about to reach 1,500 recurring patients.
Now his SEO is strong enough that Google brings him patients automatically.
Probably won't need to do marketing ever again if he doesn't want to.
He spent 12 months doing something that many entrepreneurs are too proud to do:
Getting out himself to find his patients.