Actually, the historical performance of Athens General Exchange Index confirms this rule.

FORBES: Four Flavorful Tastes Of Greece To Ride The Rebound

The rule suggests trouble: the index has fallen at an annual rate of more than 2% in the past six months.

ECONOMIST: Leading economic indicators

The index evaluates economic freedom by looking at the rule of law, regulatory efficiency, the size of government and open markets.

BBC: Hong Kong retains top spot of world's freest economy

The Index evaluates countries in four broad areas of economic freedom: rule of law, regulatory efficiency, limited government and open markets.

CNN: Which country has most economic freedom?

As a general rule, Bill Palmer, a certified financial planner at Win Wealth Management in Denver, prefers index funds or exchange-traded funds for their lower fees.

WSJ: Investors Buying Dividend Stocks for Income Are Taking On a Lot of Risk.