Many people are selling between now and the end of the year (not just stocks) to pay their gains at the CURRENT capital gains tax rates. Many will then turn around and repurchase (not just stocks) so that any future gains will get the NEW capital gains tax rate but it protects their prior gains from the new rate. Essentially it resets the clock. Past gains at the old rate, future gains at the new rate. Instead of all gains at the new rate.