“It follows that, if the appellate process is to work satisfactorily, the judgment 40 must enable the appellate court to understand why the judge reached his decision. This does not mean that every factor which weighed with the judge in his appraisal of the evidence has to be identified and explained. But the issues 6 the resolution of which were vital to the judge’s conclusion should be identified and the manner in which he resolved them explained. It is not possible to provide a template for this process. It need not involve a lengthy judgment. It does require the judge to identify and record those matters which were critical to his decision. If the critical issue was one of fact, it may be 5 enough to say that one witness was preferred to another because the one manifestly had a clearer recollection of the material facts or the other gave answers which demonstrated that his recollection could not be relied upon.”