In a complex system like market prices in real life, there are so many influences, some based upon real events, e.g. demand, economic change, and some based upon human intervention, e.g. Market Makers doing their thing by moving prices to force buying/selling. As with everything, you cannot learn or know everything about the underlying system, otherwise the markets wouldn't work at all. ED is like that too, where multi-variant calculations are used to balance our little universe. These aren't "rules". They are algorithms. You can work some out by feel, but knowing everything is impossible as you don't have all the information used to do the calculations. e.g. if production of goods is based upon the time since the last purchase, a weighted average of the demand over the past 7 days, and the relative faction influence of that particular station within the system, you can't interpret changes as you don't have those figures.
The problem is markets react to events outside their control (wars, famine, scandals)
Here for example is a daily email I get from my investment company

Now if the background game was truly dynamic and events happened in real time without any interaction in a way that cellular automata does then it would make sense, both NPCs and players could react and demand could go up based on events that happen on a daily basis.
But as we know, it doesn't work that way - Frontier have to inject stuff - so it becomes very predictable, because they have a limited set of goals. They say "Jump here" we say "How high" until we've figured it out. They say "Jump here" we say "Nahh it's not really worth it, we'll stick to these easily exploitable trade routes"