Bearish engulfing
Longers are on the offensive (price is going up) with smaller attacks (Small bull candle sticks). The bears respond by deploying a nuclear attacks, so big that engulf the size of the prior bull candle. This is enough to defeat the bulls, and the price goes down.
Bullish engulfing
In bullish engulfing , the Shorters are on the offensive launching small attacks causing the price to go down. Longers/bull launch a massive counter attack, scaring off the relinquish bears. The wining longers cause the price to go up.