All investors have a set of beliefs about how the market works, and the stimuli it responds to. These beliefs may be conscious or unconscious ones. However, there will be many times when the market does something which goes contrary to a belief. Such instances are excellent times to examine whether a belief was in fact wrong, and refresh their knowledge using the new evidence.
Barry Ritholtz has written about his own beliefs which he has revised in light of new evidence in the Bloomberg article.
One belief which many investors subscribe to is that markets' moves are closely related to economic data. However, this is very often not the case. The Guardian piece explains how the abrupt sell-offs in global markets at the end of January were in fact caused by positive economic news from the US.