But evidence really amounts to no more than expression of the opinion by a particular practitioner of what he thinks that he would have done if he had been paid hypothetically without the benefit of hindsight the position of the defendant, with a little  while the evidence of the witness is due, what in the matter of law the solicitor's duty was in the particular circumstances of the case, I should have thought, being a solicitor  the very question which the  functions, to decide.