En Bursa is a businessman. If you are participating in the stock market, he is your business partner, whether you like it or not. For your information, he has bipolar disorder.
Each day, with the exception of the weekend, En Bursa will knock on your door and presents you with an offer. On a good day, he is full of optimism and believes that the future is so bright that he will offer to purchase your stake at a premium. But when he is on the depressive mode, he sees nothing other than a dismal future for your partnership. He wants to get out of it as soon as possible. Thus, he is prepared to sell to you his stake at a highly reduced price.
The metaphor above is developed by Benjamin Graham (and localized by Yours Truly) which reflects how the stock market will radically change according to the emotion of all the participants of the stock market. Those who participate in the stock market would often find themselves caught up in waves of over-optimism. This can quickly lead to greed and, in turn, would drive the price of stocks through the roof. There are also those days where investors would find themselves weighed down by pessimism and rapidly being overtaken by fear. As a result, stock prices plummet, often to lows never seen before. We, investors, are human beings after all, and all of us are not immune to various emotions that can create havoc.