The market is right on the assumption that every investor has access to the same information. That way, the market can make a decision as a whole which dictates the shareprice - which does infact leave the market right.
The reason that shareprices change, and fluctuate from day to day in real life is based on information released, seeked and general economic conditions.
For example, AIA did jump so many % higher than the previous close, but this was based on the assumption that the Canadian Pension Plan were to rebid for the company, information not know to the market the day before - or was it, but only to a specialised few?
Another would be in this case NZO, as everybody knows, it dropped substantially after Hector, which the market decided and effectively repriced the share. It didnt fall to the lowest price straight away, as there were some investors who valued the company more at a certain point, but the market as a whole did dictate in the end which price the share should be and will continue to do so.
There is a few theories out there as to what the efficency of the market is. If anybody is interested, check out the following wikipedia write up which will help explain 'The Efficent Markets Hypothesis.' It explains the three hypothesis of weak-form, semi-strong form and strong-form hypothesis.
http://en.wikipedia.org/wiki/Efficie...ket_hypothesis
Its interesting, but we know that markets are not totally efficent as the likes of Phaedrus can still pick winning stocks through TA - against the theory EMH.
Now, I really should get back to some study...