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

What: Shares of Himax Technologies (NASDAQ:HIMX), a provider of semiconductor components for flat panel displays, soared on Wednesday after an analyst from Bank of America/Merrill Lynch upgraded the stock to "buy" from a previous rating of "underperform." At 2:30 Wednesday afternoon, the stock was up about 10%.

So what: Bank of America seems to have a love-hate relationship with Himax stock. Back in January, Himax was Bank of America's top 2015 pick among display integrated circuit providers. Three months later, the bank downgraded the stock all the way to "underperform," giving it a price target of $7 per share. Now, less than three months after that downgrade, Bank of America has changed course yet again, bringing its rating back to "buy" with a new $8.50 price target.

Chinese market share was cited as one of the major concerns three months ago, but it seems that Bank of America now believes that things are improving. Growth of 4K TV sales was also cited as a possible driver of higher margins for Himax, with the analyst estimating that over 20% of large panel driver shipments in the first half of 2016 could come from 4K TVs, up from just 3%-4% during the first quarter of this year.

Now what: Bank of America's fickleness regarding Himax offers a great example of why analyst upgrades and downgrades should never be the sole reason to buy or sell a stock. When an analyst changes his mind twice within six months, that's a sign that short-term thinking is driving those ratings.

Instead of focusing on analyst upgrades and downgrades, investors should instead look at the long-term picture and the company's fundamentals. Himax is dependent on sales of TVs, smartphones, and monitors, and the company's results will naturally fluctuate with demand for these items. What the stock is going to do over the next three months is important to speculators, not investors, and making investing decisions based on an analyst's short-lived opinion is a recipe for disaster.