Yes, maybe some gurus at a hedge fund can do it for a while. Maybe your cousin claims that he has done it. Don’t try to do it yourself.

Wall Street, and especially Morgan Stanley, with its fine exchange-traded funds, and Fidelity and Vanguard, with their super-low-cost index funds, have made it possible to be a really good investor. So have many other companies with broad-based mutual funds. You can buy domestic funds, foreign funds, foreign developed markets funds, foreign developing market funds — all at amazingly low transaction costs.

Just for my own bad self, I suggest the Fidelity Spartan Total Market Index fund (FSTVX), a very broad index fund of domestic stocks; the iShares MSCI Emerging Markets Index fund (EEM), an exchange-traded fund that invests mostly in developing countries’ markets, and the iShares MSCI EAFE Index fund, for Europe, Australasia and the Far East (EFA),which invests mostly in highly developed in Europe, Japan and Australia. This has allowed the rank amateur to take advantage of the long fall of the dollar because the stocks are priced in foreign currencies that have appreciated against the dollar.

If you feel like throwing around money speculating on individual stocks, go for it — but only after you have several millions in index and other mutual funds and exchange-traded funds and variable annuities. Just as you might stop to gamble $300 as you pass by the craps table at the Mirage on your way back from the meeting to your room, feel free to take a flier on a few stocks just for laughs. But keep it limited.

KEEP A BUCKET OF CASH Have a good chunk of cash, or near-cash, in a place like an ultra-short bond fund. Markets do fluctuate. Sometimes they fluctuate horribly on the down side for a long while. This may coincide with the time you’re fired from a job or have a child starting college or are buying a second home. It is painful to have to sell stocks into one of these down slopes. It is much better to be able to live off your cash reserves. It is even better to be able to buy during those down periods. Ray Lucia calls this approach “bucketizing,” as in keeping a bucket of cash for emergencies and opportunities.

KEEP IT SIMPLE, STUPID There are supersharp traders using computers and leverage who claim to be able to make vast sums based on strategies that will work during up, down or flat markets. They use derivatives and complex arbitrage and exotic instruments like subprime mortgage pools. (Hey, did I just say that?) Don’t try this at home. Let the Mississippi riverboat gamblers gamble. You play it safe unless you are one of those gamblers. And if you are, don’t come crying to us ants when you start to freeze in the winter.