What is the difference between a plaintiff and a court in assessing damages in a motor vehicle accident case?

In a fatal accident case, Mallett v. McMonagle, [1970] A.C. 166 at 176, [1969] 2 W.L.R. 767, [1969] 2 All E.R. 178, Lord Diplock explained the difference in this way: The role of the court in making an assessment of damages which depends upon its view as to what will be and what would have been is to be contrasted with its ordinary function in civil actions of determining what was. In determining what did happen in the past a court decides on the balance of probabilities. Anything that is more probable than not it treats as certain. But in assessing damages which depend upon its view as to what will happen in the future or would have happened in the future if something had not happened in the past, the court must make an estimate as to what are the chances that a particular thing will or would have happened and reflect those chances, whether they are more or less than even, in the amount of damages which it awards.