Trading is definetely a science but not like arithmetics, it is more complicated.
Trading deals with the probabilities which should be counted by the traders if they want to be a success and make profits. It is a common knowledge that nothing is sure in trading and there is always some probability of everything going not according to your plan. THat is why traders made up such things as money and risk management in order save their budgets from the serious losses caused by occasional fluctuations. More than that, indicatoes are also not always accurate, but they can be used to improve your trading results if you use them wisely.