Two Yale Professors want you to borrow money to invest in the stock market.

Economists Ian Ayres and Barry Nalebuff first pitched the idea in a 2005 Forbes column called Mortgage Your Retirement. Their philosophy is this: Young people should take advantage of the stock market’s propensity to deliver long-term gains by trading on margin. The daring econs explain themselves in a new book: Lifecycle Investing: A New, Safe, and Audacious Way to Improve the Performance of Your Retirement Portfolio .

Basically, the profs recommend twentysomethings use a margin account to borrow an amount equal to their cash retirement savings and invest the money for the long-run. In a recent Time Magazine interview. Nalebuff explains it this way:

…[W]e believe in stocks for the long run, but most people, when they have lots of stocks, dont have the long run, and when they have the long run, dont have lots of stocks. People seriously underinvest in the market for the first 25 years of their working life.

In theory, the concept makes a lot of sense. If an investor has the discipline to invest the borrowed money for the long run, the stock market’s long-term gains will far outpace the cost of borrowing. That’s because margin accounts can be a cheap way to borrow money. (We’re not talking about credit card rates here; in fact Ayers and Nalebuff state that this strategy is not for anybody in high-interest consumer debt).

In reality, I take issue with the strategy. Primarily, with the required discipline. Reuters blogger Felix Salmon sums up this argument perfectly:

…the amount of discipline that you need in order to successfully prosecute this strategy is absolutely enormous, and human beings tend not to be particularly financially disciplined, especially when they’re young. They’ll abandon the buy-and-hold strategy at exactly the wrong time, selling low and then buying back in at high points; they’ll start using their margin account to try to pick stocks or trade options; they’ll use any profits on expenses rather than keeping them invested and letting them compound.

Salmon concludes that the people who could take advantage of this strategy are most likely going to be extremely financially sophisticated and, consequently, will probably make tons of money in their career anyway. I agree.

You should definitely get as much money into your retirement accounts while you’re young. Take advantage of employer 401(k) matches. Max out tax-sheltered IRAs. Personally, I just wouldn’t recommend that you borrow money to do it.