VIX and the market are generally inversely correlated, meaning that, on average, VIX moves in opposite direction of the market. However, there is another key component that determines the direction of the VIX: the magnitude of the down move.

Generally, the VIX increases as there are more down days AND the magnitude of those down days increase. However, if there is a mild down day amidst the larger down days, VIX may actually decline on the mild down day because the magnitude of said down day was not as bad as recently experienced by the market.