BCS Foundation Certificate in Information Security Management Principles

An analyst insists on calculating a precise annualised loss expectancy for every information security threat, but struggles to obtain credible figures for the likelihood of a hacker intercepting company email or the damage that would result. According to the argument presented, why does the classic risk formula break down in this situation?

A security event would cause a loss of £10,000 and has a 10 per cent chance of occurring. Using the precise definition of risk described, what is the risk associated with this event?