When the market goes down – and it is bound to do so at some point – it may be a good time to invest, says Burt White, chief investment officer for LPL Financial, the nation's largest independent broker-dealer with more than 14,000 financial advisors and $542 billion in advisory and brokerage assets.

The sustained positive returns and lack of volatility that have characterized the market for months is the big story right now. But there will eventually be a dip, signaling a time to buy rather than continuing to hold, says White.

The only time since 1950 that the market saw a similar situation with a long run of good returns and low volatility was in the mid-1990s when there was nearly a year of good returns with no downturn of significance, which White defines as 3 percent.

“What may cause a pullback is extremely difficult to predict, but we are mindful of the risks across central bank policy, policymaking in Washington D.C., and geopolitics,” he says.

The Federal Reserve or other major global central bank could cause a downturn if one of them takes some unexpected action. Market leaders are anticipating federal rate hikes will remain small and incremental, but an unexpected move by the Fed could cause a pullback in the market.

Congress’s action or inaction also could have a negative effect. If there is no budget agreement and no tax reform, the markets could react negatively.

In addition, “escalating global conflicts could drive stocks lower,” White warns. “North Korea is the latest threat while relations with China have been fraying. Tariffs on Chinese goods still carry the potential to start a trade war,” all of which could negatively affect the stock market.

But if a dip occurs in this long stretch of positive returns, history tells us the market will bounce back quickly, White says.

Since 1950, stocks, on average, have pulled back 3 percent or more 4.3 times per year, and 5 percent or more 2.5 times per year. In the 203 instances, after a 3 percent pullback, S&P 500 returns were higher 77 percent of the time over the next year. The average gain after these pullbacks was 9.9 percent, higher than the overall average annual return of 8.9 percent.

“We will continue to watch central banks, policy developments out of Washington, D.C., and geopolitical tensions to attempt to get at least some warning of when the next pullback may arrive” White says. “When it does arrive, buying the dip may end up being a good strategy.”