Packing your portfolio with risky hyper-growth stocks might make you feel like a genius during a bull market, but when there's a downturn, your smile just might get turned upside down. As exciting as seeing rapidly rising share prices might be, your portfolio needs to be well-diversified, and that means you need a few companies that are stable in the face of turmoil, not to mention being capable of delivering some growth all the time. Thermo Fisher Scientific (NYSE: TMO) is a sturdy stock that's fit for holding for decades because it's one of the businesses that makes the entire biopharma sector run.