Some events are unique in nature and seem unlikely ever to occur again; others are of a kind occurring so irregularly that no reasonable prediction can be made as to the time and frequency of their occurrences.

Still others occur frequently and to many different persons; but no individual can tell when and how they will occur to him.

A general average of chances in different lines of business causes some to be called safe, others extra-hazardous.

Chance has its favorable as well as its unfavorable aspects.

Chances are averaged and added algebraically to the profit or loss in an industry, for an extra-hazardous enterprise must in general afford a higher average of profit in order to induce men to engage in it.