Investors don't get skittish every time the market wiggles. Market wiggles are of interest to traders and speculators, but not to investors. Investors either own a business they wish to own at a given price - or they simply invest in an entire market, and wait patiently over years, heedless of the bumps.
Bogle of course agrees. And Stumbling and Mumbling explains why investors should not follow market moves closely. Me? I do whatever Bob Brinker tells me to do. Never been wrong.