When I was in philosophy class before, I remember an example about tracing the thinking. The topic of the lecture is about the thinking of our human and we seemed that we are interested to trace back the path of human thinking. However, thinking is quite abstract. It is intangible. U cannot touch, see, smell, taste, listen. Therefore, some may think that what if we trace it from the other stuff which need our thinking to archive that. Therefore, they thought that playing chess may be one of the example which we can trace another's path of thinking of each other. Then, one of them moved a critical step and another cannot defeat and surrender. Then, we can conclude that the thinking of that guy is quite good , at lest is better than other. However, a problem was invoked: how did U know that guy really manage to move that critical step? How did U ensure that he was never in his luck and moved that step in blindfold? The problem here is we still cannot determine his path of thinking according to the outcome ( which is the critical move). It is because a chess master can move this step or a super lucky guy also can move this step while he is really on the peak of his lucky level....

Well...philosophy class always give U something to think. It's not so easy to have an appropriate answer. The reference for this topic can be lasted for few pages....

But I think that it may be quite easy to tell whether he is a chess master or just a lucky guy. U can just simply see whether he can take this as an advantage and then he can win at last. Otherwise, just say he 's just a lucky guy ( or dumb guy ) at that moment.