You can also look at it this way: When you get a strong signal like the breakout today mentioned above, then lots of traders go long. Then comes the critical moment: After the initial pop, do the sellers retreat or do they stay? If they stay (like today), all the traders who are long think, Oh man, if this does not scare the sellers, then nothing will, I better get out. And that's what they do. That, of course, just reassures the sellers that they are right, so they become more aggressive.