According to Keynesian economics, short-run fluctuations in output can be caused by:

In Keynesian economics, short-run fluctuations in output are closely tied to expectations about future market conditions. This theory emphasizes the impact of aggregate demand on the economy, proposing that individuals and businesses make decisions based on their expectations about future economic activity. If consumers expect a recession, for example, they are likely to reduce their spending, leading to decreased demand for goods and services, which in turn can cause a decline in output and employment. Similarly, if businesses expect future growth, they may increase investment and production in anticipation of higher demand. This connection between expectations and economic activity highlights the importance of psychological factors in influencing economic outcomes.

The focus on expectations distinguishes this concept from the other options. Long-term economic planning is more related to structural changes in the economy rather than short-term fluctuations. While changes in government policy can affect the economy, they are not the sole cause of short-run fluctuations as various factors, including consumer expectations, play a significant role. Diminished consumer confidence is indeed a factor that contributes to fluctuations, but in the context of Keynesian economics, it is better understood as part of a broader category of expectations influencing overall demand rather than being considered in isolation.