Here are some headlines you may have seen about the stock market:

  • "Stocks Jump After Strong Economic Data"
  • "Stocks Struggle Out of the Gate"
  • "Stocks Shrug Off Rout"
  • "Stocks Do Not Mean to Eat Each Other, but the Females Accidentally Bite Bits Off the Males During Mating"

OK, so that last one is from an ABC News report about giant squids. But it's not that far off the mark as investors often discuss stocks as if they're living creatures -- as if they can jump, struggle, shrug, and bite all on their own. We study their behavior, like Jane Goodall living among chimpanzees in Tanzania, hoping to discern what gets them to grow and reproduce.

But stocks are just pieces of paper (or, more often, entries in a computer) that have little inherent worth. They're human inventions that have value only to the extent that more humans want to buy them than want to sell them.

Or are they that simple?

Let's take a look at the true nature of stocks, and the care and feeding they require so that your portfolio will survive.

What moves the market?
If you own equities, ask yourself this question: Why should stocks rise?

For many investors, the answer may be that earnings rise, so stocks should rise, too. But that correlation can be pretty weak. During 2009, for instance, JPMorgan Chase (NYSE: JPM) and McDonald's (NYSE: MCD) saw annual earnings per share grow at a faster pace than their respective stocks. IBM (NYSE: IBM) and Caterpillar (NYSE: CAT), on the other hand, saw their shares perform relatively well -- but their earnings growth didn't match up, as Caterpillar actually saw earnings fall during the period.

Now, you might say that one year is too short of a time period to measure -- and you'd be right. Certainly, a number of companies were affected by the fact that 2008 earnings were relatively weak, making comparisons easier to meet.

But even stretching out the time frame may not be a guarantee of investment success. In 1999, Warren Buffett wrote an article for Fortune magazine that discussed the overall stock market. He pointed out the level of the Dow Jones Industrial Average at two points over a 17-year period:

  • Dec. 31, 1964: 874.12
  • Dec. 31, 1981: 875.00

Buffett followed by writing: "Now I'm known as a long-term investor and a patient guy, but that is not my idea of a big move." From 1964 to 1981, GDP rose 400% and revenues from companies in the Fortune 500 rose 500%, yet the price of the Dow was flat.

"Stock prices is people!"
Stocks aren't made of recycled people (unlike the food in the 1973 movie Soylent Green), but the prices are determined by human beings. After all, stocks trade on a market -- a place where buyers meet sellers and agree on a price for whatever's being sold. Pull the curtain back from any movement in a stock's price, and you'll find two people -- whether they're individual investors or representatives of an institution -- agreeing to a transaction.

If all that is true, is an investment in the stock market today solely a hope that the masses will bid up your shares? Have you gotten a load of the masses lately? Do you really want to bet your retirement on them?

At some point, you or your beneficiaries are going to sell your stocks. You invest because you want to buy something in the future. But you can't pay for a vacation home with your brokerage account statement, and stocks don't make for good eating (unlike the people in Soylent Green). You first have to sell your shares to someone else, hoping that person is willing to pay more then than what you pay now. Is that a reasonable hope?

I think it is.

Bet on things getting better
To get to the absolute essence of investing, for an issue of my Rule Your Retirement newsletter I asked several experts -- money managers, finance professors, mutual fund pioneers, and authors -- the same basic question I asked you earlier: Why should stocks rise? If it's really a market, and prices are determined by supply and demand, who's to say there will be more demand than supply in the future? Is there anything investors can hang their portfolios on other than the hope that history will repeat itself?

Their answers were fascinating. Here, I'll highlight the response of John Bogle, founder of the Vanguard Group and hero to all Fools. As he points out in his latest book, The Little Book of Common Sense Investing, from 1900 to 2005 the earnings growth of companies was virtually identical to the capital gains of the stock market. As Bogle told me, "That is in the nature of the economic system. There will be innovation and there will be efficiencies, and capital will flow to where the returns are. That is what investing is all about. There will be depressions, and things will not look good. But in the long run, capital will be rewarded."

If you think the U.S. economy -- and the world economy -- will be bigger and better a decade or two or three from now, own a piece of that growth by investing in stocks. Yes, short-term emotions will drive stock prices today and even over the next few years. But over the long term, investors come to their senses and reward the owners of stocks for being the owners of businesses that grow over time.

Of course, that doesn't mean your portfolio should be completely in stocks. And that's where one of my favorite topics – asset allocation – comes in. But that's a topic for another article. If you're not sure if you show own stocks, or how much you own, you might benefit from getting some objective, professional help. We Fools like the fee-only planners of the Garrett Planning Network, who are now offering a limited-time 10% discount to Motley Fool readers. Just click on your state on the Locate an Advisor map, and look for the Fool logo for participating advisors.

Robert Brokamp should eat more things that are green. He doesn't own shares of the companies mentioned in this article. The Motley Fool has a disclosure policy.