The market has seen low volatility and years without a major correction, writes Ben Carlson of Ritholtz Wealth Management in a recent Bloomberg article, but this doesn’t necessarily mean investors are complacent.

Carlson cites data compiled by Yale professor Robert Shiller that show investor concern regarding market valuations and a “potential market crash” are both “showing much higher levels of anxiety.” He also shares a comment from Howard Marks of Oaktree Capital, who thinks that investors are behaving in a bullish manner even though they might not be feeling bullish. “What accounts for the difference?” queries Marks. “Rates near zero,” he says, adding, “And when you live in a low return world, you have to take risk to get return.”

Carlson argues that, while in the past bull markets were surrounded by investor optimism, things seem different this time. He argues that many may not necessarily be upbeat about participating because “they’re waiting for the other side to hit in the form of a sustained market sell-off. The low interest rate environment has made it very difficult to use sentiment indicators as a predictive tool in the markets.”