" The frequent inability of curial procedures to determine
with certainty what has happened in the past, let alone
what would have been or what will be, necessarily gives
rise to a need for a number of subsidiary rules governing
the determination of the loss or injury which a plaintiff
has actually sustained by reason of a wrongful act. One
such subsidiary rule is that ... a plaintiff bears the onus
of establishing the extent of his loss or injury on the
balance of probabilities. To satisfy the requirements of
that rule, a plaintiff must, if he is to recover more than
a nominal amount in such an action, affirmatively establish
assessable damage, that is to say, loss or injury which is
capable of being measured in monetary terms ((63) See, e.g. Luna Park
(N.S.W.) Ltd. v. Tramways Advertising Pty. Ltd. (1938) 61 CLR at 301,
307, 311, 312.). In many
cases, proof of the full extent of the loss or injury
sustained will involve establishing an evidentiary
foundation for positive and detailed ultimate findings by
the court upon the balance of probabilities. There are,
however, cases where considerations of justice or the
limitations of curial method render ultimate findings,
about what would have been or will be, impracticable or
inappropriate. In such cases, damages must be assessed
on some (other) basis ... In particular, it may be
appropriate that damages be assessed by reference to the
probabilities or the possibilities of what would have
happened or will happen rather than on the basis of
speculation that probabilities would have or will come to
pass and that possibilities would not have or will not."