5% is the striking part. Most privacy tools need near-universal adoption before they meaningfully degrade surveillance heuristics. Payjoin breaks CIOH at the margins — a small minority of transactions that look like Payjoins make the heuristic unreliable for *all* transactions.

The bottleneck isn't user willingness. It's wallet support. When the protocol is invisible to the user, 5% becomes achievable. When it requires deliberate friction, it stays at 0.1%.