Charles Osenton & Co. v Johnston  AC 130, p. 130, 138, 139 per Viscount Simon L.C.:
Appellate authorities ought not to reverse the order merely because they would themselves have exercised the original discretion, had it attached to them in a different way. But if the appellate tribunal reaches the clear conclusion that there has been a wrongful exercise of discretion in that no weight, or no sufficient weight, has been given to relevant considerations such as those urged before us by the appellant, then the reversal of the order on appeal may be justified.
Per Lord Hoffmann in Biogen v Medeva  RPC 1 at p 45:
The need for appellate caution in reversing the Judge’s evaluation of the facts is based upon much more solid grounds than professional courtesy. It is because specific findings of fact, even by the most meticulous Judge, are inherently an incomplete statement of the impression which was made upon him by the primary evidence. His expressed findings are always surrounded by a penumbra of imprecision as to emphasis, relative weight, minor qualification and nuance of which time and language do not permit exact expression, but which may play an important part in the Judge’s overall evaluation.