Hi John,
In the long run the stock market goes up, but of course not every stock does. I would add that there is money to be made from long positions in almost any market environment. It's just a lot harder I bear markets. So, go ahead and look for that 25% (or whatever the percentage is), but understand that if it were easy, everyone would do it.
The reason so many investing experts say invest when the market trend is up is that they have learned from being burned enough times that they make more money being quick to follow a trend than trying to be smarter than everyone else by finding the stocks that are bucking the market trend.
That doesn't mean you can't or shouldn't take a long position in a down market but you would probably want to average into the position over time and still keep the total position relatively modest in your overall portfolio.
Individual investors often try to time the market by buying at the bottom and selling at the top. Unfortunately, no one ever knows when these will happen and too often they end up acting late, buying near the top and selling at the bottom. Developing the discipline to take partial profits as your stocks go is a good first step.
Expert advice can help you shift to a larger cash percentage ahead of a correction and help you act on an uptrend sooner than you otherwise would. That's how investors like Warren Buffett are able to make so much money.
Good luck,
------------------------------
Ed Coburn
------------------------------