How do proponents of Perseverance of the Saints have confidence in their salvation?

I was listening to a debate between Trent Horn and James White on the doctrine of the Perseverance of the Saints. In it, Trent Horn presented an argument to demonstrate that those who hold to the doctrine can’t know if they are saved. One argument against the perseverance of the saints is the citation of the thousands of people who have appeared to be fully involved in Christianity and then walked away from the faith. What the person who adheres to the PoS will do to defuse these stories is to say those people were never saved in the first place. But that means we can’t have confidence that any of us are saved, despite the fruit we exhibit! But the Bible says we can have confidence in our salvation, so PoS must be false. For a syllogistic form, see below. 1. If PoS is true, then any person *x* who exhibited belief in Christianity but walked away later was never a Christian. 2. For any person *p* who adheres to PoS, they could be a person *x*. 3. Thus, that person *p* cannot have confidence in their salvation. 4. The Bible says we can have confidence in our salvation. (1 John 5:13) 5. Thus, PoS is false.