Vanguard, the low cost index fund provider, produce some excellent research for consumers and make it available on their website. This piece on Behavioural Finance for example, talks in detail about some of the reasons why investing and wealth management can be so difficult to get right.
In essence we are programmed to think a certain way. No matter how much we know, our behaviour overrides our decision making at certain critical times. This is a universal thing. We all do it. However the difference is that we all do it, given the same circumstances.
So for example, we may all make emotional investing decisions, based on an overconfidence in being able to predict the future. This overconfidence in knowing more than someone else seems to be innate to humans in certain situations. The piece from Vanguard gives the example of how far more than a third of all drivers rate themselves amongst the top third when it comes to their driving abilities.
I believe the difference, and the benefit of using a financial adviser to make investment decisions for you, is that whilst we may all make the same irrational decisions about our own investments, we think differently when it comes to other peoples money.
I think it is easier to break from behavioural finance and make decisions based on academic research when you are advising on other peoples money and there is more than a single portfolio relying on your investing decisions.
When there is just our own money, just one portfolio we possibly rate that as less of a risk than when we see other peoples money and tens, hundreds or even thousands of investment portfolios. I believe this reality check helps advisers to make more disciplined decisions than an individual could make over a long term basis.