Investing basics tell us to "buy low" and invest in a stock when there looks to be significant upside potential. That can often be after a company gets put through the wringer and the stock declines substantially. However, sometimes it's not worth investing in a company no matter how much its shares fall.Case in point: Novavax (NVAX -2.85%) is a biotech stock down by 97% over the past three years, yet the stock still doesn't look attractive. Read on to find out why. Novavax's coronavirus efforts fell shortN ...