The blue marked candle is what we call a 'structure candle'. The market often tests the top (or bottom) of bodies of these candles. Now we only have to wait for the right entry to get into the position to ride along with this movement down. However, currently the market isn't ready yet for this short, so we wait until it does. And if the market creates price action which invalidates our possible setup, that's no problem either, since we wait for the right environment before taking the trade to maximize our chance of success.