Many traders apply indicators for their analysis in their next trade.
However, indicators formulate with historical price movement to tell us what is happening right now. It is not so much of telling us what is going to happen.
The reason is simple, it is like economic policies, can manipulate the economy figure. But it doesn't tell us exactly the expectation of the market, such as big players or hot money flow.
If you are using bollinger band on HSI the past 1 week, you would have made huge losses. Because the indicators is just using the average of previous price to plot the possible oversold point.
HSI has been in the oversold 5 days including the moment we are posting here.
Therefore, it is less efficient in telling us what is happening right now. Which is very important for trader to know what is the current big players sentiment. Rather just based on what happened before that could affect the present.
What we eat few days back doesn't mean the output will be the same as what we had few days back. (unless is constipation)