The logic of a crossover is straightforward: the fast line reflects recent prices, while the slow line covers a longer period. When the fast line moves above the slow one, the recent average has risen above the longer-term average, which is interpreted as a change in direction.
Some crossovers have established names. When a shorter moving average crosses above a longer one on a daily chart, it is called a golden cross; the opposite setup is called a death cross. The dramatic names overstate the information: both patterns lag by definition because both lines are calculated from past candles.
The main problem with crossovers is the sideways trend. When the price is chopping in a narrow range, the lines cross constantly, and each crossover is formally a signal. A series of such entries in a row consistently brings a loss, even though all the rules are followed. This is exactly why crossovers are almost never used without a market regime filter.
Several factors make the signal more useful: alignment with the higher-timeframe direction, both lines pointing the same way rather than merely crossing, and confirmation from volume. Expectations should remain realistic: a crossover describes a change that has already occurred better than it predicts what comes next.
