Dow Jones fell 300 points while the S&P 500 and Nasdaq also dipped in trading Monday morning, with one day left in what has been a record year for the U.S. stock market.

The shortened trading week due to observance of the New Year, along with thin volume, can amplify market volatility, giving active buyers and sellers an outsized impact. Plus, end-of-year trading moves where traders generally try to pocket gains while often selling losing investments to offset them can help push stocks down.