At some point, there is a sustained decline in some type of spending for some reason. (One reason may simply be that, once inventories reach their desired level, there stops being positive intended inventory investment; but there may be other reasons as well.) Then there is positive unintended inventory investment as firms are caught by surprise by the external drop in demand and they fail to simultaneously lower their production. Now inventories are too high, for two reasons: (1) They have accidentally risen, and (2) the optimal level of inventories is lower now due to the new, lower level of sustained demand. So in order to lower their inventories, firms deliberately cut back their production to below the level of demand by their customers, thus causing inventories to be deliberately drawn down—that is, intended inventory investment is negative. Intended inventory investment remains negative until the target level of inventories is reached. During this time, the economy, having peaked out, is in a downturn (a recession) both due to the sustained decrease in non-inventory expenditure and due to the negative flow of intended inventory investment.