If using bollinga band and the lower line is reached with red candle stick, with relative strength index of 30%, that indicates oversold market already, someone can  buy, but that does not mean when it hits 30% RSI, it can hit 40% RSI and the market can go up back. Also that is how is it for oberbought maker when the green candle stick hit the upper line of the band, it means oberbought market, if the RSI is at around 70%, it is better to sell at the time.

But use the money you can afford to lose because you can buy in oversold market and the price still go down further, you can also short (sell) in oberbought market and the market price continue to increase. This happened especially during high volatile market. Trade with the amount you can afford to lose.