New York (CNN Business) Good news! American consumers are feeling about as bullish as they have been in nearly 20 years, thanks in large part to a healthy job market.

The Conference Board reported Tuesday that its index of consumer confidence is near 18-year highs. This follows a similar report from the University of Michigan earlier this month, which showed that consumer sentiment was at its best level since 2004.

But here's some potentially bad news — for investors at least. Consumers are notorious for being overly optimistic at the top of the market cycle.

So the high levels of confidence on Main Street may once again signal tough times ahead for Wall Street. That trend may already be under way now as stocks pull back because of trade war concerns.

Maximum optimism = maximum prices?

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