Venture capital investments usually have very high minimums, which can be a challenge for some investors. Find an investing pro in your area today. Maybe more. If you have the time, the magic of compound interest and the Rule of 72 is the surest way to double your money. Short Selling Definition Short selling occurs when an investor borrows a security, sells it on the open market, and expects to buy it back later for less money. Related: How to Hire a Financial Advisor. Back Classes.