If theory never matches reality, what then is the point of theory? Why not act according to the light of pure reason? Because theory provides a framework in which to think and marshal one’s thoughts, before judgement and instinct decide whether the particular occasion is one in which to follow conventional theory, or to disregard it. And because trained instinct and experience are far better guides than reason, which is never “pure” but always conditioned by the frame of mind which you happen to adopt.
There are of course rules in advocacy; for example, “never tell a jury what verdict they ought to reach”. And the corollary of that rule is that it is sometimes shrewd to leave the jury to complete the last link in the chain of an argument, because they will then find the argument so much the more convincing, and be more willing to act upon it. But rules like these ought to be second nature; you ought not to have to think about them. More in the conscious mind should be the rule, that it is unwise to say too much beforehand about how you intend to cross-examine a witness; because you may find that any inspiration about how to conduct the cross-examination has then gone. Much better to keep what inspiration you have for the moment when you cross-examine. It is as though it is a work of art, and your creativeness can only be expressed once. Even after it is all over, you may not fully appreciate what you have done, but you have got your result. This is particularly so, if much of the cross-examination is improvisation. No plan is likely to last beyond the first significant answer; but if you have planned thoroughly you are able to improvise with relative safety.
Whether the mechanism of genetic evolution is cumulative selection, or not, is of no relevance to this situation. Some knowledge of how the mind works, a slight instinct for the witness’s sticking points, his vanities, his unwillingness to lose face, might be helpful. But to conclude from the discovery that the world of genetic change is virtually mechanical, that there is no Deity, is to ignore everything that lies in between; the world of morale which Napoleon considered crucial in War, human endurance and a sense of duty, courage or cowardice, strength of character or the lack of it, whether in the depths of his soul a man is an optimist or pessimist, are all bypassed, as though they did not exist. Only if you proved that all these are illusions, and that the whole world of the mind and spirit is mechanical, would you be entitled to conclude that there might not be a God; but then your argument itself would be mechanical, like a child repeating something parrot-wise, and you yourself would have no judgement to decide whether it was a good argument, or a bad one. All you would be able to do is goggle at a meaningless ritual; and what would be the point of doing that?