Suppose the Spot ask exchange rate for Canadian dollar, S"($/CAD), is $0.90 = CAD1.00 and the Spot bid exchange rate, Sb($/CAD), is $0.85 = CAD1.00. You have $10,000 and you think you need to exchange for some Canadian dollars to visit Canada. One minute later after you purchased them, you think you would rather visit Mexico so you don't need Canadian dollar anymore. If you sell these Canadian dollars then, how much of your original $10,000 would be "eaten" by the bidask spread