Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

August is a bit of an odd month. U.S. stocks have had a hard time putting together just two winning days in a row so far this month. The S&P 500 (SNPINDEX:^GSPC) didn't achieve it today, retreating by 0.5%, while the narrower, price-weighted Dow Jones Industrial Average (DJINDICES:^DJI) lost 0.7%. This is quite unlike the "clockwork rally" we have witnessed for much of this year, which has had a knack for producing streaks.

Today's losses were enough to see the CBOE Volatility Index (VOLATILITYINDICES:^VIX), Wall Street's "fear index," gain nearly 6% to close just above 13. (The VIX is calculated from S&P 500 option prices and reflects investor expectations for stock market volatility over the coming 30 days.)

Aftertaste: The Apple pop
It appears that yesterday's "Icahn pop" had some legs, as Apple (NASDAQ:AAPL) bucked today's trend in the technology sector, gaining another 1.8% versus a loss of 0.4% for the Nasdaq index. Intraday, the shares even managed to trade above $500 for the first time since Jan. 23, the day on which the company announced disappointing fiscal third-quarter results (causing 18 analysts to take a bite out of their own price targets for the stock).

Today's price increase makes a total gain of nearly 5% since Carl Icahn disclosed via Twitter that his firm had taken a position in Apple shares, or $20.6 billion added to the company's market capitalization. That's quite a tribute to Icahn's reputation, particularly when one considers that his ownership interest is reportedly much less than 1% of the company (it's roughly one-third of a percent). For more on the significance of Icahn's presence in Apple's capital, please refer to my article from yesterday.

Ackman on his failure at J.C. Penney
And speaking of activist investors, it's become quite fashionable to bash hedge fund manager Bill Ackman these days (including by Carl Icahn, who has become a bitter rival), although, truth be told, he bears a good dose of responsibility in the matter. However, having just watched his full interview with Charlie Rose, in the wake of his resignation from the J.C. Penney (NYSE:JCP) board, I didn't feel as if I wasted my time. Ackman is highly articulate, and he summed up the root cause of his disastrous foray at ailing retailer J.C. Penney in a single sentence:

"There was more risk in J.C. Penney than pretty much every other investment we've made, because of the nature of the changes that were required."

J.C. Penney's turnaround is far from assured -- the risk Ackman refers to persists today (although the stock price is lower, which makes for a greater margin of safety). That's something investors who are tempted by the shares would do well to remember.

Fool contributor Alex Dumortier, CFA, has no position in any stocks mentioned; you can follow him on LinkedIn. The Motley Fool recommends and owns shares of Apple. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.