The Peter Lynch philosophy of “Buy what you know” is something I tell people all the time. What it means is, when you want to invest, you should invest in companies that make the products or deliver the services you use every day. From a psychological point, it can help you stay invested and interested in companies.However, sometimes those companies that you know and love are not rocking and rolling the way they used to. Sometimes, there’s an underlying shift in the core business that you may not be aware o ...