Losing Streaks Are a Feature of Randomness, Not a Malfunction

[Shadow Trader]

A strategy winning 60 percent of trades will still lose five in a row at some point. The probability of five consecutive losses starting at any given trade is 0.4 to the fifth power, about 1 percent. Across hundreds of trades, such a run becomes likely rather than remarkable.

A useful rule of thumb is that the longest losing streak in a sample of N trades grows roughly with the logarithm of N. With a 50 percent win rate, a run of seven or more losses becomes plausible somewhere within a few hundred trades.

Planning should assume streaks exist. Sizing that survives ten consecutive losses without breaching a drawdown limit is far safer than sizing tuned to the average experience. At 1 percent risk per trade, ten straight losses cost roughly 9.6 percent of the account.

Streaks also tempt psychological errors: abandoning a valid system after a normal cold run, or increasing size to recover quickly. Defining in advance what a normal losing run looks like for the strategy turns a stressful event into an expected one.