Warren Buffett regrets not investing in Google and admits that he was "too dumb" in the past about Amazon’s potential.

These are just two of the startlingly candid comments from the 86-year-old "Oracle of Omaha," almost universally regarded as the world’s greatest investor of all time, given to shareholders at Berkshire Hathaway’s [his company] annual meeting on Saturday.

It’s refreshing to hear someone as successful as Buffett sharing his investing mistakes – because we can all learn from others’ missteps, especially when they are true-pros or mightily successful, such as Buffett the Investment Legend.

I’d suggest that almost all serious investors, including myself of course, have made previous investment mistakes that could have been easily avoided.

For this reason, last year my firm carried out an international survey to discover millionaires’ top three investment regrets.

The most cited mistake was failing to appropriately diversify portfolios. Other errors included not investing earlier, focusing too much on the short-term, being emotional over investments, and not keeping enough cash in reserve.

Ensuring your portfolio is properly diversified is one of the fundamentals of successful investing.  Yet it is surprising how many people fail to do this.  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.

All too often even experienced investors focus heavily on the short term and there are many disadvantages to this. Typically, a short-term investment strategy involves considerably higher risks, compared to investing over a longer period.

Other pitfalls of a short horizon include that investors can often sell a quality investment too early due to over focusing on short-term valuation metrics. Alternatively, they may sell an investment if it drops in the short term, meaning that they would then miss out on it potentially growing steadily in the longer term with increasing returns.

Stock market performance is fairly predictable over the longer-term – they usually go up. 

For this reason, investing in equities is recognised globally as one of the optimum ways to accumulate wealth over long periods.  If you put off investing you are likely to miss out on the long-term benefits you could have been gaining.

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. 

Objectivity is key.

In addition, not having kept some powder dry is another common error highlighted by many investors. It is always advisable to have some cash at the ready and be prepared to use it should a clear trend and/or opportunity present itself.

All this could make it sound like investing is somewhat perilous.  Yet nothing could be further from the truth – not investing is probably more dangerous over the longer-term. 

This is evidenced by the fact that most of the world’s wealthiest people are themselves dedicated investors. It is just a question of being sensible, taking proper advice and, where possible, learning lessons from others to avoid the obvious mistakes. This is why we conducted this poll.

As Warren Buffett highlighted, even the most financially successful people on Earth make mistakes and can cringe at their errors when they look back.

But it is worth learning from such people so we learn the valuable lessons from them and try and avoid the financial pitfalls for ourselves.

Nigel Green is founder and CEO of deVere Group. One of the world’s largest independent financial advisory organizations, de Vere does business in 100 countries and has more than $12 billion under advisement.