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.

The stock market was full of optimism today, as seven out of 10 sectors, and six out of 10 individual stocks, locked in gains. Unfortunately for the worst performers in the stock market today, they weren't invited to the ball. Hopefully, one day they'll at least be able to mope by themselves around the punch bowl, but that wasn't in the cards for these three materials companies on Monday. The S&P 500 Index (^GSPC -0.78%), which briefly hit all-time highs in today's session, finished up 11 points, or 0.6%, to end at 1,847.

Shares of United States Steel (X -0.79%) ended at the depths of the S&P today, shedding 3.4% in trading. Unlike retailers or tech companies that have the freedom to innovate and differentiate their products from competitors, U.S. Steel is chained to a commoditized product, steel, which means its customers have little more than price to consider when choosing where to buy from. Right now, U.S. Steel, and domestic steel producers, in general, are in a tough spot, because Chinese steel is far cheaper. That price discrepancy -- which sat at nearly $160 a ton last month -- became even more dramatic today as Chinese media reported a slowdown in real estate-related lending, which should curb demand for steel, and send prices even lower.

Agriculture and chemicals behemoth Monsanto (MON) also saw its stock wilt today, losing 3.1%. Monsanto has found itself in the crosshairs of organic food enthusiasts in recent years, as the pioneer in genetically modified organisms, or GMOs, strong-armed its way to agricultural ubiquity. While Monsanto can go to court with farmers all day long about genetic seed disputes, it's far more difficult to hold sway with entire nations, given the degree of international backlash over GMOs.

Lastly, Cliffs Natural Resources' (CLF 0.39%) stock fell 2.9% today as the coal and iron ore producer felt the unpleasant results of the ripple effect that began with reports of slowing Chinese real estate lending. Although I often blame flap-happy Asian butterflies for bouts of miserable weather in the U.S., linking Cliffs Natural Resources' Monday slump with a news story in China isn't as hard to explain. As mentioned, U.S. Steel suffered on Wall Street today because of a report that China's hitting the brakes on real-estate lending, lowering demand for steel. Thus, since iron ore and coal are vital ingredients in the steel-making process, Cliffs, by extension, will see lower demand for its wares, all things being equal. I'm still working out the math behind my butterfly weather theory, so stay tuned.