A good analogy is to think of the economy as a still lake. If you throw a rock into it, you know that it will create concentric circles of waves. You throw a second rock and you know that its waves will interfere with the first. But now the waves create oscillating patterns and now they hit the irregular shore and pretty much immediately you have the usual chaotic pattern of waves all over the lake.
It's the same deal with the economy. We can predict the first order, maybe the second order consequences of our actions. But again and again we're faced with a highly dynamic system with an almost infinite set of variables and we seem continuously surprised when things get out of hand.
To me, a federal reserve system that insures banks from bank runs makes sense. This sort of FED that we have now that tries to control the overall economy is - to me - at least as hopeless as centralized 5-year plans under communism.