They might need the cash for a big personal purchase, such as a new house or an expensive boat. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price. Other times they sell because they think their stock is overvalued by the markets and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge on their sector and they might think that an economic slowdown is in the cards. But they only buy their own shares for one reason: They think the stock is a bargain and has tremendous upside. The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher doesn't mean it will happen. Insiders can have all the conviction in the world that their stock is a bargain, but if the market doesn't agree with them, the stock could end up going nowhere. Related: 5 Silver Mining Stocks Poised to Rebound At the end of the day, large institutional money managers running big mutual funds and hedge funds drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity and why it's twice as important to make sure the trend of the stock coincides with the insider buying. Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, warranting a closer look at these stocks. Here's a look at a number of companies whose insiders have been loading up on their own stock recently per SEC filings.