The coin lands heads 60.0% of the time. Choose a side, size your bet, and see what over- or under-betting the edge does to a bankroll — including asymmetric reward:risk payouts.
This setup echoes a well-known 2016 experiment by Haghani and Dewey, in which participants were given a real bankroll and a coin they were told would land heads 60% of the time — a genuine, sizeable edge. Despite that edge, a large share of players still went bust, mostly by betting far more than the edge justified, switching sides after a few losses, or chasing losses with bigger stakes. The lesson isn't just "the math has an optimum" — it's how easy it is to abandon that optimum under pressure, even when the odds are known and in your favor.
This version adds an adjustable reward:risk payout so you can model asymmetric edges — low hit-rate / high payoff strategies, not just even-money coins. A 30% win rate at 3:1 can still be +EV; Kelly sizing changes with both probability and payout.
A 60% coin is generous, though — it's a teaching device. Most real trading edges are nowhere near that clean. Discipline means sizing every trade the same principled way without inflating after wins or abandoning after losing streaks — both ways of quietly giving up the edge you're trying to harvest.
The hardest skill isn't finding an edge — it's telling the difference between "this losing streak is just variance" and "my edge is actually gone," and behaving correctly under each.