Thanks to you guys who have posted a reply to this question.
It is always interesting to me how individuals evaluate the answer by different ways of thought.
The answers that you guys gave are all in some way related to the fact that you already have established in your mind what you need to do in order to catch fish. But before you were able to make that call you had to have had some period of time fishing to form that answer, and that is the basis of the answer that l would give to this question, Experience, for without that you would not be able to give the answers as you did.
Dealing with a specific fish feeding activity, reading water, entomology,
knowledge of flies to use, casting and presentation skills and so on are all related to experience and the learning of skills.
The other single factor l would assess is simply this,, knowing the habits of the creature you pursue, regardless be it fish or game. The man who posesses that indifinable skill of afinity to ward that intent will no doubt reap the rewards more so than another.
The great fun of that is of course aspiring as we do to become proficient at what we do, part of our human nature.