Why do casinos convert your money into chips for you to "play" with? It's because they want you to forget, to some degree, that you're gambling with real money. By making it more abstract, they can get their patrons to spend more and take on more risk.

I think the same effect is present in the stock market, and in our wallets. Think about what's in your pocket or handbag: probably some cash and a credit card or two. If you're thinking about using your cash for a purchase, you probably deliberate a little more than if you're thinking about using your credit card. With the plastic, you can quickly charge it and forget it, and your cash reserve will appear unchanged. 

That's how many people end up mired in credit card debt, and it's how companies such as Discover Financial Services (NYSE:DFS), Capital One Financial (NYSE:COF), and Visa (NYSE:V) have made millions. (Don't despair if you're one of those crushed by debt. You can dig yourself out of debt. Many Fools have paid off tens of thousands.)

Meanwhile, with stocks, we send in checks to fund our brokerage accounts, but after that, we sometimes start thinking of our investing as a big game. I've heard people talk about "taking a flyer" on this or that stock, about getting in on "the game," about how they're "betting" on this or that happening. They seem to forget that they're dealing with their hard-earned dollars, that their retirements and dreams are at stake.

Think also of when you're down considerably on a given stock. If you bought Citigroup (NYSE:C) or VMware (NYSE:VMW) a year ago and now find yourself down some 70%, you might be inclined to stubbornly wait to make all your money back on these stocks. But hold on -- if you think Citigroup is in for a world of hurt over the coming years, and you have very little understanding of the virtualization software that VMware develops, you might do well to sell and move your money into companies you understand well and have great confidence in.

Don't think of any stock as a game you want to win. Instead look at the big picture, and make sure you're putting your dollars where they have the best chance of growing for you. And remember that the money in your brokerage account is very real, and can grow over time into a sum that will serve you well in retirement.

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article. Discover Financial Services is a Motley Fool Inside Value recommendation. VMware is a Motley Fool Rule Breakers selection. Try our investing newsletters free for 30 days. The Motley Fool is Fools writing for Fools.