Le Chatelier's principle says that if a system at equilibrium is disturbed, the system will shift in the direction that:

Le Chatelier's principle in plain English: a disturbed equilibrium pushes back. If you add more reactant, the forward reaction speeds up to consume some of it. If you raise temperature on an endothermic reaction, equilibrium shifts forward (absorbs heat). The system never amplifies the disturbance, never stops, and rarely runs to completion.