When there is an increased amount of reactants, the system shifts in favour of the products. When there is an increased amount of products, it shifts to the reactants. That's fine and good.
But when a different substance is added, for example,
CoCl42- (aq) + 6H2O (l) <---> Co(H2O)62+ (aq) + 4Cl- (aq)
has AgNO3(aq) added to it, the system shifts in favour of the products.
Can someone please explain to me why this happens?