The psychology behind a bullish engulfing is a sudden power shift from sellers to buyers, where fear flips to confidence in a single session.
The first candle reflects steady selling that pushes price lower in a downtrend, then in the next session buyers step in aggressively, driving price higher and covering the entire range of the previous red candle.
The pattern reflects a change in the balance of power from sellers to buyers, suggesting the market is moving from pessimism to optimism.
Short sellers cover, sidelined buyers pile in, and the resulting candle visually broadcasts that bearish conviction has broken.