I do not assert that either one or the other of these persons was condemned guiltlessly, or that such “side issues” have no value and ought not to be proved. I merely point out that caution is necessary in two directions. First of all, these side issues must not be identified with the central issue. Their demonstration is only preparatory work, the value of which must be established cautiously and without prejudice. It may be said that the feeling of satisfaction with what has been done causes jurists frequently to forget what must yet be done, or to undervalue it. Further, a psychological examination must seek out the motives which led or might have led the accused to deny some point not particularly dangerous to him. In most cases an intelligible ground for such action can be discovered, and if the psychologically prior conditions are conceived with sufficient narrowness to keep us from assuming unconditional guilt, we are at least called upon to be careful. This curious danger of identification of different issues as the aim of presentation of evidence, occurs much more frequently and with comparatively greater degree in the cases of individual witnesses who are convinced of the principal issue when a side issue is proved. Suppose a witness is called on to identify a man as somebody who had stabbed him in a serious assault, and that he has also to explain whether the quarrel he had had with this man a short time ago was of importance. If the suspect is desirous of having the quarrel appear as harmless, and the wounded person asserts that the quarrel was serious, the latter will be convinced, the moment his contention may be viewed as true, that his opponent was really the person who had stabbed him. There is, of course, a certain logical justification for this supposition, but the psychological difficulty with it is the fact that this case, like many others, involves the identification of what is inferred with what is perceived. It is for this reason that the mere fact of arrest is to most people a conviction of guilt. The witness who had first identified A as only the probable criminal becomes absolutely convinced of it when A is presented to him in stripes, even though he knows that A has been arrested on his own testimony alone. The appearance and the surroundings of the prisoner influence many, and not merely uneducated people, against the prisoner, and they think, involuntarily, “If he were not the one, they would not have him here.” Section 24. (b) Causation.[129]