supply and demand
Prices move because of supply and demand. When demand is greater than supply, prices rise. When supply is greater than demand, prices fall. Sometimes, prices will move sideways as both supply and demand are in equilibrium.
Market psychology plays a major role as traders and investors remember the past and react to changing conditions to anticipate future market movement.
In the financial markets, prices are driven by supply (down) and demand (up) excesses. Supply is synonymous with bearish, bears, and selling. Demand is synonymous with bullish, bulls, and buying.