Basically the most complex thing people do is communicate. Making a computer understand it is not easy. As an American living in Germany I can say that it took me 6 years (in country) before I could talk with someone while someone else talked near me about something else. It is REALLY hard to sort out the words from the static without being able to predict what words should come next and without understanding the context of the conversation or being able to hear the really subtle parts of the speech. Even native speaker will pause and ask the other speaker if the meant A or B in some situations in others we can just infer the meaning and the missing words but even then we make lots of mistakes. Now lets make a computer that can do this without mistakes!