Diversification

If a perfect system existed, everyone would use it and the market would cease to fluctuate.

The upside of your system is that if you're right, you'll clean up; the downside, you might wake-up one morning and find that much of your net worth has disappeared.

[Peter666]

"the downside, you might wake-up one morning and find that much of your net worth has disappeared."

The likelihood of this happening with certain individual stocks are almost nil. You have a much greater chance getting hit by a bus on the way to the bank.