If you have only $5 in your pocket as this month's disposable income, there is no investment vehicle for turning that into $10. Besides putting it in a bank where it will lose value due to inflation, gambling may be the only non-zero investment opportunity available to you.

On the other hand, if you have $5MM in your pocket, there are tons of investment opportunities for you to choose from, from treasury bills to angel investing, limited only by your appetite for risk. You have an entire financial services industry that exists for the sole purpose of helping you turn that $5MM into $10MM.

Larger sums of money are easier to invest in ways that will provide meaningful returns, and doubling your money is inevitable over the long term. In comparison, that $5 will probably turn into a meal or other short-term benefit.