  I have often wondered why AI could never cross the barriers of sci-fi and become a reality when it sounds so logical. Why could we never realize anything that AI promised when the scientists first proposed the concept?
The crux of the problem lies in the very definition of the concept itself. If intelligence were to be definable and a process could be established for achieving the same then why would we ever have a mediocre person in the world. Isn't it very obvious that there is no practical all encompassing definition of intelligence yet??!! Why do we even try to analyze intelligence as an entity as compared to it being an attribute. Is intelligence related to the development of the brain? Is it related to pure exposure and the whims and fancies of hebbian learning?! If it was, then how and why do we distinguish between two regular students of the same class? It is plain simple that intelligence cannot be algorithimized. It is at best describable in terms of patterns of thoughts through the brain whereby a better quality of intelligence optimizes the result better.
How could a thought pattern be defined then? Why can't two thought patterns be similar? They could be similar only when the guiding principle of genetics of the organism is similar. Now coming back to the primordial question - why have we not been able to realize AI? Because we never tried to understand how the brain works in conjunction with the genetic code of the organism. We always tried to generalize the behavior of the brain and tried to mathematicalize based on assumptions of what a complex system like it could function like. Another approach tried was of trying to understand how the brain learns logic and trying to package it in a generic form as a form of intelligence.
The answer to true AI does not lie in generalization but in the realization of the fact that genetic variance and control applied to the evolution of the each unique system such as an artificial brain is one of the most logical approaches to closing the gap between the artificial and the real masterpiece of nature - the brain! 
