Amid all the of doomsday predictions and fearful hand-wringing about the stock market, the knowing chuckle of billionaire investor Warren Buffett once again puts panic into context.

Of course he's buying stocks. Prices are falling, so why not? Like with his famous “hamburger quiz,” the best time to buy any asset is when it's cheaper, not when it's more expensive.

As stocks fell last week, Buffett was buying. He was likely to buy anyway, he said. Lower prices just made it easier. “I like buying it as it goes down, and the more it goes down, the more I like to buy,” Buffett told CNBC.

The typical Buffett quote that gets trotted out in turbulent markets applies: “Be fearful when others are greedy and greedy when others are fearful.”

For retirement investors, though, there's another, more apt quote. “Only when the tide goes out do you discover who's been swimming naked.”

Apt because the first quote relates more to how traders think. If you have a strong conviction on an investment and others seem to hate it, then buy without hesitation. If everyone loves a stock you own, watch out.

Getting it wrong

Retirement investors, however, should never be trying to figure out what the market “thinks” about a given investment. That's market timing, a high-risk endeavor. Every time you get it right and make money, there's the unavoidable risk of getting it wrong and losing even more.

Like a gambler, you find yourself in the hole pretty quick, taking bets with increasingly poor odds in an attempt to rebuild your pot. The math quickly begins to work against you.

For example, if you lose 10% of your money in an investment, you don't need a 10% “win” to get back to even. No, you need 11%.

Say you have $10 invested and it loses 10%. Now you have $9. Hold that investment and it might come back.

But if you sell (through market timing) and reinvest in something else, a 10% rebound doesn't help. You get back to $9.90 that way. You actually need a tad more than 11% to truly recover the loss.

Assume you manage to earn 11%. Great! Now you must pay commissions, fees and taxes. You could achieve your number, then slide backward into single digits on trading expenses alone.

Cash out at a market bottom, as so many do, and it's likely that you'll never get back to even. A 50% decline on $10 puts you at $5. If you sell and then reinvest, a subsequent 50% gain gets you only to $7.50. What you really need is a 100% gain.

October market

If you're not a market-timer—and no long-term investor should be—then the “swimming naked” quote is more relevant.

Yes, there are plenty of people who should be worried about the near-term direction of stocks. Mostly, these are professional money managers.

The reason they have to worry is because they are paid to worry. If their particular strategy is falling apart, there are real consequences—lost clients, lost fees, lost prestige. It's a career killer.

Retirement investors, however, should be squarely in Buffett's camp. Lower prices are good. Let the short-termers panic as the tide recedes. For us, a falling stock market is nothing more than another opportunity to buy.

Can the market fall even more? Sure it can. Catastrophically so? It can't be discounted. But we recovered from 2008 and from the dot-com collapse, and we will rebound in due time from whatever the market has in store.

Having a long-term view requires you to own the right mix of assets for your goals, not for the market of the moment. The tide will roll in and out, as it does. Yet it need not be a stressful time—unless your suit has washed away in the surf.