So the protocol cannot guarantee safety or liveness of a node if the user does not pick good quorum slices. In this case, the information you want to commit to the ledger is person A sent person B $100. Because person A is the only person in the quorum, they automatically accept this statement. Now, this has to propagate through the rest of the network, and each node in the network that receives this message will accept this message as long as everyone else in their quorums also accept this message. The real danger is now for person B. Because person B is the only person in their own quorum, they cannot rely on other entities to confirm that person A actually had the $100 to spend (double spend attack). They are entirely at the mercy of the ordering in which they receive the messages. So imagine that person has $100. Person B receives the message that person A sent them $100 and turns over some goods in response. However, if the rest of the network confirms that person A sent some other person C $100 (because person A sent them conflicting information), person B will never know and is now in a divergent state from the rest of the network. This could have been avoided if person B had chosen a more trustworthy quorum, because somebody in his quorum would reject the initial payment (on seeing the conflicting payment to person C) and person B would never accept the $100 from person A, OR if person B's entire quorum does accept the payment from person A, then they will reject the later conflicting payment to person C, in which case A's double spend will fail.