What is the meaning of "fons et origo mali" in the context of a motor vehicle collision case?

In terms of judicial expression, the governing passage applicable to this case is found in Walker v. Brownlee, 1952 CanLII 328 (SCC), [1952] 2 D.L.R. 450 (S.C.C.). Cartwright J., writing for the majority, stated: While the decision of every motor vehicle collision case must depend on its particular facts, I am of opinion that when A, the driver in the servient position, proceeds through an intersection in complete disregard of his statutory duty to yield the right-of-way and a collision results, if he seeks to cast any portion of the blame upon B, the driver having the right-of-way, A must establish that after B became aware, or by the exercise of reasonable care should have become aware, of A's disregard of the law B had in fact a sufficient opportunity to avoid the accident of which a reasonably careful and skillful driver would have availed himself; and I do not think that in such circumstances any doubts should be resolved in favour of A, whose unlawful conduct was fons et origo mali.