Final answer:
A very pessimistic outlook by firms regarding future business conditions that leads to reduced investment spending causes a leftward shift in the aggregate-demand curve, resulting in lower output and higher unemployment in the short run.
Step-by-step explanation:
When firms become very pessimistic about future business conditions and consequently reduce investment spending, the short-run effect on the aggregate-demand curve will be a leftward shift. This is due to a drop in investment, which is one of the components of aggregate demand—the total amount of goods and services demanded in the economy at a given overall price level and in a given time period. Investment is a major component of aggregate demand, so a significant reduction in investment spending will reduce aggregate demand.
The leftward shift of the aggregate-demand curve represents a decrease in total spending, which leads to lower output and employment in the short run. According to the AD-AS (aggregate demand - aggregate supply) model, a steeply sloping aggregate demand curve indicates that changes in price levels do not have a large effect on the quantity of aggregate demand. Nonetheless, a shift in the curve itself, such as one caused by a change in investment sentiment, results in a movement to a new equilibrium point with potentially lower output and higher unemployment.
The economic impact of a pandemic provides a real-world example of such a scenario, where aggregate demand can be severely affected, as seen with reduced consumer spending on services like restaurants and travel, and firms curtailing investments due to an uncertain future. Overall, a more pessimistic outlook leads to reduced economic activity and a contractionary effect on the economy, as depicted by the leftward shift in the aggregate-demand curve.