Tipping Point: What is a value trap?

A lot of times, when the markets are falling, investors think that valuations of some stocks have become more attractive, and they proceed to invest in them. However, many such stocks remain at low levels for a very long time, or do not recover at all even when the markets do. This could be because the fundamentals of those stocks have got permanently damaged. When you invest in such stocks, you are said to have fallen into a value trap
 
What should investors do?

It is not enough to use simplistic filters to pick stocks. You can't buy