I thought this very interesting, courtesy of Thomas Ingoglia, paraphrasing noted technician Gary Anderson:

"A market bottom usually has the weakest bouncing the hardest." "However AFTER THE BOTTOM, relatively strong stocks need to be strong. when we get stronger stocks getting weaker while weaker stocks are getting stronger, traders are being defensive and unsure of themselves. It is a much better sign when traders are putting all their money in leaders that have already made runs. It says that they feel the market is strong and safe"