In physical world, likelihood is based on historical frequencies, scientific calculation like path of hurricane, engineering specification such as MTBF (Mean Time Between Failure). Likelihood is the foundation to predict when an event will occur. It is the key catalyst in the insurance industry.
In cyber world, this is not going to be the same. Uncovered vulnerability will turn security protection insecure over night. An example is TLS (Transport Layer Security). People take TLS for granted as a secure means to protect sensitive information submission over the network. The Heartbleed suddenly shocked everyone and this can’t be predicted per traditional manner. A different approach has to be adopted to address cyber risk likelihood.