Assuming a price is set on an free market there are particular difficulties to pricing. A free market is one where the price is entirely determined by the willingness of people to buy and sell at a particular price point. What you perceive as price, is actually the "tick", i.e. the quote of the last transaction.
The first and most serious major obstacle to pricing is a variation of the prisoners dilemma, a psychological phenomenon. For instance, bitcoin might be worth 4$ now, but you believe it will be worth 5$ in 3 days. Will you buy bitcoin? If acting only on your conviction, yes. But what if you consider what other people will do? Will others believe bitcoin will be worth 5$ in 3 days? Will they act on their conviction? Will the others believe that others believe that it wil be worth 5$ in 3 days, and will the others believe that the others who believe will act on their conviction? Will the others believe that others believe of still others who believe that they will act on their conviction? It goes on like this ad-infinitum.
The actual behavior of any individual on the market is essentially chaotic and unpredictable (for the reason stated above and others).
This is related to a phenomenon you call market efficiency. An efficient market always reflects the optimal price-point at any given time. If that is so, then you cannot win on this market, because at the time you would have to realize a competitive edge, everybody else has already acted on that information.
Markets are not 100% efficient of course. But modern electronic markets can be very, very efficient (as say compared to stock markets fro 100 years ago, where you could get a competitive edge just by having access to a fast courier).
What makes matters rather more difficult for price forecasting is that not only are humans engaging in the market, machines are as well. The machines may not be terribly good at what they do, but they are terribly fast. The machines that work well (i.e. don't loose much) will survive, and the ones that don't will die in short order. Since speed is one of the major benefits of the machines over humans, they tend to make markets even more efficient.
Another phenomenon to price forecasting is that of information and entropy. Suppose you found a reliable method to predict a market at a given time. You act on this information and indeed you make a profit. The profit you will be able to achieve will diminish over time until it reaches zero or reverts. The reason for this is that you acted on private information, which you leaked out by engaging in a trade. The more successful you are in exploiting your forecast, the better you train every other market participant to react to their losses. Since for every trade you make successfully, there has to be somebody who lost. People or machines who lose on markets usually exit those markets in some fashion. So even if the other participants are not adjusting their behavior, your success is weeding out those with the wrong behavior.
Yet another difficulty in pricing forecasts are black-swan events. Since information can have a huge impact on pricing, the sudden appearance of new information can throw a conservative forecast completely off the rails and incur huge losses (or huge unexpected benefits). You cannot quantify black-swan events in any shape or form.
It is my belief that you cannot predict efficient and well working markets. You might be able to predict some very sub-optimal markets, but usually, hedge-funds are always on the hunt for inefficient markets to exploit, so by simple decree of market economics, the inefficient markets tend to be a perpetually dying species.