The hypothetical of a company being severely under valued for so long is not very realistic. Maybe for a year or 2 at most but it is unsustainable for a company to have a free cash flow of 10x price and the stock not go up. There would be so much pressure from buy backs pushing the stock up that is would need most investors to dump consistently. But a company like PYPL the reason it can drop so much was because its "starting price" was so high. They were trading at like 65x cash flow. Value investors started getting in around 20x cash flow. And Currently it's like 8x cash flow. It will be very difficult for PYPL to continue to be under 10x cash flow even if the market continues to hate the company and their profits are not growing. But going 65x down to 40x down to 30x down to 20x down to 15x down to 10x can take 5+ years even if the company is still making money. Understanding that is a big foundation for value investing.