I find it a strange choice to explain double-entry bookkeeping with the example of "one entry for Alice, one entry for Bob". That's really not what it's about. It's obvious that a transaction with two parties could be recorded in two places, but to me the crucial point of double-entry bookkeeping is that it requires two entries for each party of the transaction . So if Alice buys book from Bob, four entries are made.…
For example, a bank might decide you likely can't pay your loan and write it down to zero. You might still have the liability on your books because you plan to repay it. They'll make the relevant entries in their system (and the debits and credits will balance) and you'll do nothing (which balances).
Double entry bookkeeping has zero to do with other entities. It's solely about your own books.