This retail giant just keeps growing, decade after decade.When investing in a stock, you should always make your choice with the intention of holding on to it for a while. That's basically what distinguishes long-term investing from day trading and playing the market. Beyond long-term investing, there is the idea of forever investing, where you buy stocks that you never plan to sell, regardless of any rough patch they may hit. My forever stock is Walmart (WMT +0.12%).One reason I'm never selling Walmart sto ...