102 years ago this month, Germany declared war on France, kicking off World War I.

Fueled by its victory over France in 1870, the Germans had spent decades coming up with a plan developed by Field Marshall Alfred von Schlieffen. The goal was to achieve a quick and stunning victory against France, Germany’s biggest adversary. The plan was to then quickly move troops to the East to fend off a likely Russian invasion.

To achieve that goal, Germany decided to avoid its shared border with France. Instead, it would move through Belgium. While doing so meant bringing other powers into the fray against Germany, namely the United Kingdom, it also meant avoiding strong French fortifications.

When the plan was executed in August 1914, the Germans swept through Belgium and got within 50 miles of Paris. But their plan was stalled by an early Russian attack, the British Expeditionary Force, and French resolve. The Schlieffen plan nearly, but didn’t, come to pass. The end result was a 4-year stalemate. While the last World War 1 veteran passed away in 2012, the scars of the trenches can still be found in the French frontier.

We all make plans in our lives, big and small. But things rarely go to plan, especially once in operation. In a war, one party’s plans are susceptible to be thwarted by the enemy’s counter-moves. Such can be true in life as well.

In investing, the plan is usually simple: to make a great return on your money. The plan usually isn’t executed well. The average investor, broadly speaking, tends to underperform the market average. It’s no surprise that index investing has become so popular.

When you’re earning the market average (before expenses), you’re in the middle of the herd, and likely to earn close to the market’s long-term gains as well. It’s slightly better if you can do so with a 401k plan or other investment structure with a tax-advantage and potential matching. If so, it’s the lowest risk way to get the market’s return.

But that plan has a big flaw. The market’s return sounds great over time. But it includes all the years the market is down. If you can stomach a 30-percent-plus drop, like the 2008 market dive, then you should do well over time. But everyone is different, and anyone looking to retire within a few years of such an event may have to seriously reconsider their plans.

So, whatever financial plan you have, make sure it’s flexible. Markets move in unpredictable ways, and being able to make rapid changes, even if it means having to take a painful loss now, can save a fortune so your capital can live to fight another day.

For instance, I went short the oil market in late 2014 following OPEC’s decision to continue to maintain oil production. It meant taking some losses on energy stocks I owned. But, as oil prices continued to slide further, the put options I had bought continued to make a profit for me. 

I know most investors only want to stick with one side of the market—usually the long side. If that’s the case, then your decision isn’t to just be long, it’s how much or your money you want invested and how much should stay in cash.

It’s still a great time to raise cash. Last week, all three major U.S. market indices, the Dow, the Nasdaq, and the S&P 500 hit record highs. The last time all three did so simultaneously was in December 1999, right before the tech bubble burst. I don’t know what the next market crisis will look like, only that there will be one. Things don’t move up in a straight line, and market rallies don’t continue forever. Cash is a valuable cushion.

That’s why your plan should include strategies like covered call writing. That allows you to stay invested, but generate some extra income. The only “risk” is possibly getting called away from an investment you own at a price you already determined as fair.

We looked at that investment strategy last week. It should be enough to take the sting out of most market downturns. If you can get the equivalent income of a few extra dividend payments and keep the shares thanks to a market selloff, you’ve improved your returns without having to go heavily towards cash.

But a market downturn is also a good time to consider the market’s next move. It’s the perfect time to identify the market’s worst recent performers with the best chances of doing well going forward. Thanks to these opportunities, which always exist, there’s always opportunities for those willing to dive into individual stocks.

Thanks to the three near-10-percent selloffs we’ve had in the market in the past two years, many individual companies aren’t helping the markets reach those new highs. That’s where the bargains are now, and where investors can expect the best returns going forward.