Why the market is unstable at consumer equilibrium?

Answer 1

There are many reasons why a consumer market equilibrium may be unstable, and it depends on which school of economic thought you follow. Generally, if there actually is a consumer equilibrium (which some believe does not truly occur) then what will cause it to become unstable is the effect of random shocks:

I.e.) let future consumption for any period be ct+j = ct + Et.

E is a random shock variable which is normally distributed around the mean (which we'll assume to be 0). Consumption in any period is simply equal to consumption in the period of time = t plus whatever shocks occurs in the economy (i.e.) political unrest, social movements, oil crises, etc.). In an economy, small shifts in variables such as consumption can cause larger changes because once an economy moves away from equilibrium, it causes a resulting change in other key equations which is no longer optimal. How the economy restores to equilibrium is also a debate amongst economist: Keynesians believe that wages/prices are 'sticky' and thus equilibrium is slow to reoccur after a shock; classicists believe that wages/prices are not sticky so that equilibrium will reestablish itself quickly. The rate at which an economy corrects these shocks will also affect how unstable equilibrium is. Finally, equilibrium can also constantly change due to factors such as technological growth. The economy needs time and information to adjust to these new equilibria and this can cause instability.