15.2 Risk and Return (double)

Risk & return go hand and hand, so much is obvious. But how do we define risk and how can you determine your risk on different levels?

One could say that pricing and the fluctuation of shares are a result of supply and demand. 
A share can rise in value by 20% in just one day without any change of its fundamentals. There are, however, several models to define the theoretical value of a share.