Housen v. Nikolaisen,  2 S.C.R. 235,  S.C.J. No. 31,
2002 SCC 33, at para. 8.
 The requirements of, and purpose behind, the doctrine of
res judicata were thoroughly canvassed in Danyluk v. Ainsworth
Technologies Inc.,  2 S.C.R. 460,  S.C.J. No. 46, 2001
SCC 44. In that decision, Binnie J. reviewed the historical development of the doctrine and its component parts: cause of action
estoppel and issue estoppel. He also reviewed the development
of the doctrine of collateral attack.
 As set out in Danyluk, at para. 25, the preconditions to the
operation of issue estoppel are ( i) that the same question has been
decided; ( ii) that the judicial decision which is said to create the
estoppel was final; and ( iii) that the parties to the judicial
decision or their privies were the same persons as the parties to
the proceedings in which the estoppel is raised or their privies.
It is clear that those three preconditions are met in this case.
 However, Binnie J. went on in Danyluk to point out that
the court retained a discretion not to apply the doctrine where to
do so would work an injustice. More specifically, Binnie J. adopted
the observation in British Columbia (Minister of Forests) v. Bug-
busters Pest Management Inc.,  B.C.J. No. 1043, 159 D.L.R.
(4th) 50 (C.A.), where Finch J.A. said, at para. 32:
It must always be remembered that although the three requirements for
issue estoppel must be satisfied before it can apply, the fact that they may be
satisfied does not automatically give rise to its application. Issue estoppel is
an equitable doctrine, and as can be seen from the cases, is closely related to
abuse of process. The doctrine of issue estoppel is designed as an implement
of justice, and a protection against injustice. It inevitably calls upon the exer-
cise of a judicial discretion to achieve fairness according to the circumstances
of each case.
 Binnie J. added, at para. 67:
The objective is to ensure that the operation of issue estoppel promotes the
orderly administration of justice but not at the cost of real injustice in the
 Finally, Binnie J. concluded with a statement of what he said
was the most important factor in deciding whether issue estoppel
ought to be applied in any given case. He said, at para. 80:
As a final and most important factor, the Court should stand back and, tak-
ing into account the entirety of the circumstances, consider whether applica-
tion of issue estoppel in the particular case would work an injustice.
 The exercise of the discretion to apply issue estoppel was
also the subject of the decision of this court in Minott v.
O’Shanter Development Co. (1999), 42 O.R. (3d) 321,  O.J.