Explain why most investors prefer to hold a diversified portfolio of securities as opposed to placing all

Question:

Explain why most investors prefer to hold a diversified of securities as opposed to placing all of their wealth in a single asset. Use an illustration of the feasible and efficient sets to explain your answer.
Portfolio
A portfolio is a grouping of financial assets such as stocks, bonds, commodities, currencies and cash equivalents, as well as their fund counterparts, including mutual, exchange-traded and closed funds. A portfolio can also consist of non-publicly...