Wealthy investors say failing to diversify their portfolios was their largest investing mistake, according to a recent survey.

According to Zurich-based deVere Group, which surveyed clients with more than $1 million in investable assets, 27 percent of the clients reported failing to diversify as their No. 1 investing mistake.

The firm’s CEO, Nigel Green, said in a release that most investor mistakes, including failure to diversify, are easily prevented with professional advice.

“It is surprising how many people fail to do this,” Green said. “Having a well-diversified portfolio across asset classes, sectors and regions means you are best placed to mitigate risks and best placed to take advantage of important opportunities.

The respondents cited other errors as well. Twenty-three percent of them said that their mistake was not investing earlier. Another 20 percent said they had focused too much on the short term, while 15 percent said they had been too emotional about investments. Eight percent said they had not kept enough cash in reserve.

The key, said Green, is to start investing as early as possible, and to remain objective throughout the experience. “Making decisions based on heartfelt emotions and loyalty are admirable traits in most parts of life, but not when it comes to investing. Investment decisions based on pure emotions, such as fear, greed or the desire to follow the crowd, amongst others, can be disastrous.”

The firm polled 652 clients in the U.S., the U.K., Asia and Africa.