The Dow Jones Industrial Average (DJINDICES:^DJI) was down 89 points at 1 p.m. EDT Wednesday, after Goldman Sachs (NYSE:GS) CEO Lloyd Blankfein appeared live on CNBC and warned investors about the downside risk in today's markets.

Specifically, Blankfein called today's calm, steady markets a "luxury," and warned investors that any number of events could instantly end the current ride.

This market is calm?
Over the past year, the S&P 500 (SNPINDEX:^GSPC) is up just over 18%. Over the past six months, the index is up 7.8%. Over the past three months, it is up about 3.5%. That's about as steady as a market can get. 

For investors, that steady movement from the lower left to the upper right of the following chart has been the status quo for five years now. The index is up 107% over that time. 

^SPX Chart

^SPX data by YCharts.

That's pretty crazy, which is exactly Blankfein's point
To hammer his point home, Blankfein pointed to several uncommon conditions today that could each individually derail this 62-month (and counting) bull market.

The big one? Interest rates.

It is no secret that interest rates today are exceptionally low. That can't last forever, and when the Federal Reserve's near-zero rate policy does end, the reverberations will be felt throughout the economy.

The cost to borrow money will rise, making it more difficult for businesses and individuals to achieve desired returns on investment. Existing variable rate debt will cut into profits as interest expense rises. Bond portfolios across the board will be reset because of mark-to-market accounting as the value of today's low-rate bonds will lose value in a higher rate environment.

Politics, both at home and internationally, could also end the Dow's hot streak.

Goldman Sachs CEO Lloyd Blankfein. Source: Company website

On Tuesday, Eric Cantor, the No. 2 Republican in the House of Representatives, was defeated in his primary election against a Tea Party-backed challenger. We don't do politics here at The Motley Fool, but this surprise defeat is worth noting in terms of the bigger picture risks that could derail the market.

The memory of the government shutdowns, fiscal cliffs, and budget deficit crises is still fresh in the minds of many political and investing pundits. Another politically manufactured crisis could be exactly the event to derail the markets.

Blankfein's point was not political, it was about risk management. Over a long enough time horizon, crazy things will happen, especially in politics.

Internationally, the potential for a market-shaking event is just as large. So far the Dow and S&P have shrugged off the risk of greater Russian aggression in Eastern Europe. Just because those geopolitical shocks haven't roiled the markets yet, though, doesn't mean they won't in the future. Again, the point is that it's a risk.

When will this bull market end? 
There is no way of knowing with any certainty when this bull market will end. However, it will eventually come to a close.

The best way to time the market is to not even try to time the market.

Don't go out and build a bomb shelter in your backyard; instead, keep a level head and make rational decisions for the long term. Focus on finding amazing companies at attractive valuations and investing in them for five years or longer.