Why Over-Diversifying Can Cost Us Dearly

Taking the principle of portfolio diversification too far can ruin your financial future.

The content of this article was relevant at the time of publishing. Circumstances change continuously and caution should therefore be exercised when relying upon any content contained within this article.

You’re reading a free article with opinions that may differ from The Motley Fool’s Premium Investing Services. Become a Motley Fool member today to get instant access to our top analyst recommendations, in-depth research, investing resources, and more. Learn More.

Diversifying a portfolio is a risky strategy.

By diversification, I mean buying, say, 20-plus different investments with the aim of mitigating the effect of potential losses.

That’s a dangerous approach to investing, which could lead to lacklustre returns at best or, worse still, capital loss over all.

I thought we are ‘supposed’ to diversify!

Traditionally, many see a diversified portfolio of shares as a defence against individual company risk, but too many shares in a portfolio can actually increase risk.

With too many shares, it’s hard to know the underlying businesses well. Do-it-yourself investing can be hard work. We need to follow the operational and strategic ups and downs of our investments and keep a finger on the pulse of valuations and investor sentiment if we are to distinguish investing from gambling.

Many of us private investors don’t do our investing full-time, so how can we keep tabs on 20-plus investments in our portfolios? Keeping up with ten investments at one time, my personal maximum, exhausts me, and I’m much more comfortable with around five. That’s still diversification, but it’s effective diversification because there’s much more chance of making well balanced, considered and timely ‘buy’, ‘hold’ and ‘sell’ decisions, and thus greater chance of building wealth through investing.

Diminishing focus

If we take on too many investments, there is risk that the quality of our choices might decline. With many holdings, we could end up chucking in a few speculative ones with hardly a thought, or relaxing our buying criteria, or failing to develop a well thought out rationale for buying.

When over-diversification diminishes the percentage of our capital allocated to any one decision, there is great risk that we diminish the quality of our decision-making similarly. Even if a determination to avoid such pitfalls exists, time constraints could mean we end up falling into that trap anyway.

With greater focus on just a few shares, it’s more likely that we will be on top of opportune moments for buying and selling. Initially operating with between five and 10 equally weighted investments can provide diversification whilst at the same time providing us with a realistic opportunity to build wealth through investing.

Those first five shares or investments will be our best ideas. Number 32 will, arguably, be down in the third-division of ideas and operate as an expensive and time-consuming distraction, as it sucks our attention from our best investments.

A long tail

Many investors don’t equally-weight their investments, instead, lending a nod to the ‘best idea’ theory, which sees greater allocation of capital to a ‘top five’ or a ‘top 10’ or some such; I used to do that a few years ago. However, that long tail of tens of smaller positions could be doing more harm than we realise. Those positions, that have minor effect on our portfolios, dissipate our attention. Such diffusion of attention could cause us to miss a vital cue in one of our larger holdings, which could prove costly.

If our first five to 10 investments truly are our best ideas, why not slough off that long tail and concentrate focus on just those five to 10? I did, around three-and-a-half years ago, and my overall investment performance improved.  

If we are holding 20-plus shares in a portfolio, shouldn’t we really ask ourselves if we’d be better off with a tracker or a fund?  If we have 20-plus small-cap holdings, for instance, why not buy a fund that tracks the small-cap index? Doing so would reduce the costs and time-input required and probably deliver a similar result to holding a wide diversification of 20-plus equally weighted positions in our own portfolio.

Conviction buying

I’m not going to diversify away my advantage as a private investor. Wide diversification of 20-plus or more investments makes little sense when so many trackers and funds are available as an alternative today. Over-diversifying in our own portfolios is risky because it takes our eyes off the important balls.

If we are involved in the stock market with the aim of building wealth by our own hand, we need to concentrate on backing quality decisions with meaningful amounts of capital. If we do that, the greater intensity of focus can lead to reduced risk anyway, without the need to attempt to protect ourselves, from ourselves, by over-diversifying.

More on Investing Articles

Asian man looking concerned while studying paperwork at his desk in an office
Investing Articles

A stock market crash feels like it might be imminent

Conflict in the Middle East means a stock market crash feels like a real possibility right now. But being ready…

Read more »

Rolls-Royce's Pearl 10X engine series
Investing Articles

Should I buy Rolls-Royce shares as they march ever higher?

Rolls-Royce is making billions of pounds a year and looks set to do even better in future -- so what's…

Read more »

Smiling family of four enjoying breakfast at sunrise while camping
Investing Articles

£1,000 buys 110 shares in this UK beverage stock that’s smashing Diageo 

Shares of Tanqueray-maker Diageo are languishing at multi-year lows. So why is the stock behind this tonic water brand on…

Read more »

UK financial background: share prices and stock graph overlaid on an image of the Union Jack
Investing Articles

What next for Aviva shares after a cracking set of 2025 results?

Aviva achieving its 2026 financial goals a year ahead of schedule has got to be good for the shares... oh,…

Read more »

This way, That way, The other way - pointing in different directions
Investing Articles

Should I buy stocks or look to conserve cash right now?

In a market dealing with AI uncertainty and conflict in the Middle East, should investors be looking for stocks to…

Read more »

Investing Articles

Here’s how many British American Tobacco shares it takes to earn a £1,000 monthly second income

Is an AI-resistant business with a 5.38% dividend yield a good choice for investors looking for a second income in…

Read more »

Black woman using smartphone at home, watching stock charts.
Investing Articles

1,001 Barclays shares bought 12 months ago are now worth…

Barclays shares have delivered excellent returns over the last year. But can the FTSE 100 bank keep outperforming? Royston Wild…

Read more »

Two business people sitting at cafe working on new project using laptop. Young businesswoman taking notes and businessman working on laptop computer.
Investing Articles

Get started on the stock market: 3 ‘safe’ shares for beginner UK investors to consider

Kicking off an investment portfolio on the stock market may seem like a scary prospect. Mark Hartley details a few…

Read more »