Some handicappers believe incorrectly that, if they play a negative expectation game, they will lose a percentage of their initial bankroll equivalent to that expectation. This is incorrect.
For example, assuming that the expectation of randomly betting favorites at Track X is -17% and that Joe Punter starts with a bankroll of $1,000, he expects to lose (randomly betting favorites at Track X) $170 (17% * $1,000) over a season. In fact, he can expect to lose 17% of his total bets (turnover), not of his initial bankroll. Suppose he makes 250 flat $30 bets on favorites giving him a total turnover of $7,500 ($30 * 250), he can expect to lose $1275 (17% * $7,500) - not $170! In other words, he stands to lose (on average) $275 more than his initial bankroll!