What does "a widely held belief" mean?
In an article, it talks about the pierce fluctuation of a high-tech company. The share price varied from $1 to $40, then $8. The summary of this article is that the company's performance exemplifies a widely held belief.
My question is that does "a widely held belief" mean the belief from the crowd and show up in the stock market. Further, the "exemplify" means an example?

Question

What does "a widely held belief" mean?
In an article, it talks about the pierce fluctuation of a high-tech company.  The share price varied from $1 to $40, then $8.  The summary of this article is that the company's performance exemplifies a widely held belief.  
My question is that does "a widely held belief" mean the belief from the crowd and show up in the stock market.  Further, the "exemplify" means an example?

Answer

"A widely held belief" is something that is believed among the majority of people. This belief may or may not be true, but, in spite of that, it is believed to be true by most people.

"exemplify" means to make an example of something. So, in your sentences, the company performance makes/gives an example of a "widely held belief."

I hope this helps. If you are still unsure, please let me know.