Credibility. Trotter Estate
In Trotter Estate (Ont CA, 2014) the Court of Appeal allowed an appeal against the dismissal of a summary judgment motion where the hearing judge dismissed critical evidence without explaining why it's credibility was impugned:
Where important issues turn on credibility, failure to make credibility findings amounts to reversible error: see Sagl v. Cosburn, Griffiths and Brandham Insurance Brokers Ltd., 2009 ONCA 388 (CanLII),  O.J. No. 1879, at paras. 98-100.. R v D.H.
In this criminal case, R v D.H. (Ont CA, 2016), the Court of Appeal discusses the adequacy of a judicial reasons for adverse findings against the credibility of a witness, and their treatment on appeal:
 A trial judge’s assessments of credibility are accorded very considerable deference on appeal, as long as the trial judge has sufficiently explained how significant discrepancies that could undermine credibility and reliability have been resolved. This court recently reiterated that principle in R. v. M. (A.), 2014 ONCA 769 (CanLII), 123 O.R. (3d) 536, at paras. 17-19:
[W]here a case turns largely on determinations of credibility, the sufficiency of reasons must be considered in light of the deference generally afforded to trial judges on credibility findings. It is rare for deficiencies in a trial judge's credibility analysis, as expressed in the reasons for judgment, to warrant appellate intervention: Vuradin, 2013 SCC 38 (CanLII),  2 S.C.R. 639, at para. 11; Dinardo, 2008 SCC 24 (CanLII),  1 S.C.R. 788, at para. 26. While a trial judge is not required to resolve every inconsistency in the evidence, the trial judge “should address and explain how she or he has resolved major inconsistencies in the evidence of material witnesses: G. (M.) (1994), 1994 CanLII 8733 (ON CA), 93 C.C.C. (3d) 347 (Ont. C.A.), at p. 356; R. v. Dinardo, 2008 SCC 24 (CanLII),  1 S.C.R. 788, at para. 31”: M. (A.), at para. 14. As the Supreme Court stated in R. v. Dinardo, at paras. 26-27, the failure to articulate how credibility concerns are resolved, particularly in the face of significant inconsistencies in a complainant’s testimony, may constitute reversible error, as an accused is entitled to know why the trial judge is left with no reasonable doubt.
Nevertheless, the failure of a trial judge to sufficiently articulate how credibility and reliability concerns are resolved may constitute reversible error: Vuradin, at para. 11; Dinardo, at para. 26; R. v. Braich,  1 S.C.R. 903,  S.C.J. No. 29, 2002 SCC 27 (CanLII), at para. 23. After all, an accused is entitled to know why the trial judge had no reasonable doubt about his or her guilt: R. v. Gagnon,  1 S.C.R. 621,  S.C.J. No. 17, 2006 SCC 17 (CanLII), at para. 21.
Similarly, we take it as self-evident that a legal error made in the assessment of credibility may displace the deference usually afforded to a trial judge's credibility assessment and may require appellate intervention.