It's been said many times before but, given how few people pay attention, it's worth repeating every time that the market takes a nosedive. History has demonstrated amply that investors who try to jump in and out of the market to avoid big declines find themselves achieving horrendously bad results than those who simply buy and hold.

I know -- with the Dow looking like it could open down 500+ points tomorrow, it can be scary. And maybe you'll be able to save yourself more anguish by dumping everything. But maybe not. It's impossible to know and the track record of investors who make that bet during market meltdowns is not good at all.

Bottom line: If you're in a panic over the market's gyrations today, do not trade! Take a walk. Play with your kids. Read. Go to the gym. Whatever! But making investment decisions in a state of emotional instability is never a good idea.

If the market's volatility is messing with your mind, I would strongly urge you to pick up a copy Your Money & Your Brain for some strategies on how to manage your emotions. So go pick up a copy, turn off your computer, shut off CNBC, stuff the Wall Street Journal in the trash, and chill out.