Over the long run, stock markets are fairly efficient. In the shorter term, however, valuations can go to extremes both on the low and high sides. Investors usually create these anomalies by piling into whatever is currently in vogue and indiscriminately selling whatever is out of favor.
When industries fall out of favor, Wall Street sometimes drives the market cap of companies within that sector far below what an acquirer would pay for the entire company. That leads to buying opportunities for discerning investors with the patience to wait for the industry to right itself. Of course, it’s anyone’s guess when the tide might turn—investors may need to suffer through years of under-performance before these investments eventually pay off. It’s often well worth the wait, however.