Shares of Stryker Corporation are trading higher on Friday. A story about a suspected Iran-linked hack across devices hit the stock hard.

Despite the unusual and surprising news, the stock still followed a predictable pattern. This is why Stryker is the Stock of the Day.

Some analysts and investors believe that markets are not predictable. They believe that markets follow a random walk and that the past can not be used to predict future movements.

These analysts are wrong. They don't understand how markets work.

One thing about markets that isn't random is how there is a tendency for a stock or a market to find support at a price that had previously been support. See Stryker’s chart: below

Back in April, a number of the investors and traders who sold shares of Stryker at around $328 regretted doing so when the price rallied. Unhappy sellers vowed to repurchase their shares at the same price at which they sold.

So yesterday, when the stock dropped back to around $328, they placed buy orders. The large volume of these buy orders formed support at the price that had previously supported. This wasn't random or a coincidence.

Another thing about the markets that isn't random is a stock's tendency to revert to the mean. If something goes too far in one direction, there is a good chance it will reverse and head back in the other direction.

The red line on the chart above is two standard deviations below the 20-day moving average. 95% of trading should occur within two standard deviations of the mean. If a stock falls below this threshold, it is considered oversold.

This will draw buyers into the market. They will be expecting a reversion to the mean or a move higher. Their buying may push the price up.

Successful traders know markets are not random. Understanding important price levels and reversion to the mean are two ways they profit.

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