Anarchism can only exist when there's a single individual not interacting with any other person, period. Every human interaction immediately breaks any sort of anarchism, there will always be some agreed upon behavior, whether implicit or explicit, violently enforced or not.

I suppose most ancaps are actually minarchists, or "minimal state" proponents, because capitalism fails terribly without laws and some way to enforce them. Without a state (even as small as a group's leadership), "ownership" doesn't exist, whoever's stronger owns the thing. You blink, you lose. You die, it's first dibs. Fell for a scam? Too bad, you should've been smarter. Got captured and sold into slave labor? Too bad, you should've seen that coming. Someone stole your stuff? Too bad, you should've secured it better.