appraising how joseki relate to the rest of the board—hence knowledge of joseki is regarded as shallow, when compared with the ability to integrate a strategy into a complex game landscape. There is a go proverb that states that "learning joseki loses two stones in strength," meaning that rote learning of sequences is not advantageous. Rather learning from joseki should be a player's goal. Hence the study of joseki is regarded as a double-edged sword and useful only if learned not by rote but rather by understanding the principles behind each move. Every joseki should be used as a specific tool that leaves the board in a particular shape. Just as using an improper tool in machinery can be devastating, choosing the wrong joseki can easily be worse than improvising one's own moves. In his book A Way of Play for the 21st Century, Go Seigen compared choosing the proper joseki to choosing the proper medicine—pick the right one, and you feel better. Pick the wrong one and you die.(par.) Rui Naiwei similarly remarked that playing joseki is easy [but] choosing the right one [in a game] is hard.(par.) A joseki may fall out of use for various reasons, some of which may often seem minor to the amateur player, and professionals may consider one variation suboptimal for a very specific reason. There is no definitive guide to what is joseki; the situation with joseki dictionaries is similar to that of natural language dictionaries, in that some entries are obsolete and the listing is not likely to be complete. Studying joseki is only an important part of developing one's strength as a player at some levels; the study of life and death and middle-game fighting are considered to be more important. Concepts Opening theory is less dominant in terms of study for those wanting to reach a good amateur level, than in chess or shogi. It is, however, an important component of Go knowledge, though there is no single, codified source for it. The standard sequences for the joseki in many cases come to a definite end, after which both players should move elsewhere. In some cases a sharp local struggle breaks out, which neither player should neglect. For those cases, the result of the opening may develop out of a 10×10 corner area into the rest of the board. Analysis without taking into account what other stones are in