What’s your best strategy for financial investments today? Some of your stocks are on life support (techs, dot-coms, telecoms). Some stocks shot up while you weren’t looking (natural gas, HMOs). Business has suddenly slowed and a new financial policy team is moving to Washington, D.C.

As an investor, you start with one fact: No one no one knows what is going to happen to stocks.

Ten years ago, the economy was emerging from a mild recession. Many analysts predicted sluggish growth for years. Suddenly, in the middle of the decade, everything took off like a rocket.

Back then, the change took us by surprise (although we’ve forgotten that the matter was ever in doubt).

We’ll be just as surprised by what happens during the next 10 years. Every time you think you’ve finally learned rules, someone changes the game.

As investors, we habitually confuse strategies with outcomes. Outcomes are pure hindsight. Strategies are decisions you make when you don’t know what the outcome is going to be.

In hindsight, you should have been invested in tech stocks that is, until last March.

As a strategy, however, you need to diversify over the entire market, because you have no idea which stocks will lead the next wave up. It could be techs again but different techs not the ones that you own now.

Individuals can’t and don’t diversify when they buy individual stocks. You’d have to own 50 stocks or more, of different sizes and in different industries.

In real life, we tend to buy the most popular stocks, representing the industries that have recently done the best. We wind up with all our money in just a few sectors, without even thinking about it.

Even if you take a stab at three or four unpopular stocks, you might pick the ones that get even more unpopular or don’t gain as much as the market as a whole.

That’s why I like mutual funds for your serious, life-changing money. Not narrow funds that buy only certain industries, like techs and telecoms. Instead, buy the well-diversified funds, which own techs, telecoms and all the other sectors, too.

Principally, that means index funds, which follow the market as a whole.

Without question, some investors won life-changing money in recent years by speculating in individual stocks. But if you doubled and redoubled your bet in techs, Nets and telecoms, last year’s Nasdaq crash wiped out a good part of your gain.

If you own high-risk stocks that run up, you should take part of your money off the table so it’s yours to keep. Gamblers who keep throwing the dice eventually lose.

It’s always possible that the Nasdaq mania isn’t over yet. But that’s not a good bet. It leaves you bare if your assumption turns out to be wrong. Here are some of the things we’ve come to consider “true,” which might not work as well in the future as they did before:

– Buying the dip (meaning buying a popular stock that drops in price). Whether that’s smart depends on which dip you buy. Stocks don’t always shoot back to their previous highs.

Before buying a stock that drops in price, you should learn more about why it dropped and what the outlook for that specific company is. Most of us don’t have a clue another good reason for buying mutual funds.

– Momentum investing (buying stocks that have been moving up). That’s an easy approach for amateurs. You don’t have to analyze the stock or even know what the company does. You just follow the herd.

But herds don’t run forever, as you learned last year.

Traditionally, market leaders “rotate” from one industry to another. That’s harder for individual investors to follow.

– Growth investing. Growth stocks that still flaunt super-high price/earnings ratios will be hard-pressed to outperform the general market in the years ahead. That’s a historical fact. In ordinary times, most stocks don’t excel once their P/E ratios exceed about 60.

The so-called value stocks good companies beaten down in price do the best when the economy slows.

– Do-it-yourself investing. It’s a lot harder to pick stocks once financial manias pass. That’s another reason to reconsider mutual funds.

Syndicated columnist Jane Bryant Quinn can be reached in care of the Washington Post Writers Group, 1150 15th St., Washington, D.C. 20071-9200.