Market psychology sets market prices. It is based on investor perceptions of the moment. It has a 'will-of-the-wisp' quality. It is always at work in one direction or another with investors chasing themes believed to produce portfolio gains.
Oil prices ((WTI)) vs. companies exposed to industrial sectors in the US provide a good example of the impact of market psychology. With the emergence of computer driven algorithms in the past 20yrs, more capital has been shifted with correlated price trends than ever before. The need for execution speed and quarter-over-quarter performance measurement, even day-vs-day performance