odds
The house edge
The rule
In a game where the pot shrinks each round, the average player must lose. Only a real, measured edge survives the costs taken from every trade.
Where it flips
But a real, tested edge can beat the house's cut. The point is not that trading cannot be won, but that it cannot be won without one. The error is assuming an edge exists because a few trades worked, instead of measuring it against the full drag of costs.
Thorp thought like a gambler who only played when the odds were truly in his favour, and refused to play when they were not. Trading derivatives loses money before skill even enters. Brokerage, securities transaction tax, exchange fees, and the buy-sell gap are taken from the pot on every leg. Because F&O trades have several legs and lots of turnover, these costs pile up. The player with no measured edge is, by the maths, the one funding everyone else.
A worked example
A reader breaks even on their trades before costs across a busy quarter and feels they are holding their own. Adding up brokerage, STT, and buy-sell gaps across hundreds of legs turns that flat result into a clear net loss for the quarter. [illustrative]
How to spot it
- ·costs left out when checking whether a strategy works
- ·many legs and high turnover, each adding fees
- ·a claimed edge never measured against brokerage, tax, and the buy-sell gap
Edward Thorp · A Man for All Markets