I have observed the markets for several years. For these liquid markets, the price almost always move back and forth. If you don't take stop loss, there is a high likelihood price will come back in two weeks and your position become profitable. But most people end up take loss and then chase another "hot" market.
What is the chance for price continue moving up and not test 3960-4000? Very slim. After SPX moved beyond 1000, it went down to 750; after it broke 2000, it went back to 1800; after above 3000, it went back to 2200; and it is just a matter of time for the price to go back to 3200-3500. Not sure exactly when:)