Guy Adami, stocks editor at OptionMonster.

I have been upfront in my view that the market had been set up for a move to 900 since the S&P 500 closed above 741 a couple weeks ago. However, part of my trading strategy was a re-evaluation if the S&P closed below 800.

Well, today is preparing for that scenario.

Some days are easier than others, and today is one of the hard ones. Hard because the market is forcing us to make a decision prior to the close. As of this writing, the S&P is down some 29.6 points, trading below 790. Waiting until the close to make a trading decision on a day like this can prove to be extraordinarily costly as there is a chance the market will continue to slide lower.

Today's action is forcing us to make a decision right now. As difficult as it is to do, I would say that trimming half of your long positions at these levels might be prudent. Of course, there is a chance that we reverse and move back to the 800 level in the S&P today, but there is an equally good chance that the move lower accelerates.

Action is always better than non-action on days like today. Don't get caught up in what I call "paralysis by analysis." Doing something on a day like this is infinitely better than curling up in the fetal position and falling back on the strategy of "hope."

As my friend Jeff Macke is fond of saying, "Hope is not an investment thesis." So you might want to consider trimming long positions under the premise that we will close below 800 in the S&P and will probably test 741 again on the downside.

This could set you up nicely to re-establish long positions instead of stopping out of long positions if we get to 741. Keeping your powder dry is critical.