Private investment means putting your own money at risk in anticipation of realizing a gain later; public “investment” means taking and spending someone else's money to support your idea of how you think they should live, or to satisfy the special interests that help get you reelected.A company or individual that takes their own money and uses it to help another business or individual is known as a private investor.Some private investors also help individuals who cannot secure a mortgage or loan through a bank. The investor will negotiate the terms of the investment.Private investment (or induced investment) depends upon expected profitability or marginal efficiency of capital which, in turn, depends upon future expectations that are often fluctuating violently.Hence, private investment becomes highly capricious it is very high in boom periods and low in the period of depression.A private investor is a person or company that invests their own money into a company, with the goal of helping that company succeed and getting a return on their investment. The long answer: The field of private investment is more varied than the short answer might make it seem at first.