But people still manage to ruin it.
Diworsification is what happens when you keep adding “diversified” investments and end up with:
- higher fees
- more overlapping holdings than you realise
- more admin and more decisions
- no meaningful reduction in risk
It looks sophisticated. It often performs worse.
What diworsification looks like in real life#
Common patterns:
- owning multiple “global” ETFs that mostly hold the same US mega-caps
- adding a new fund for every market headline (tech fund, AI fund, healthcare fund…)
- stacking managed funds with similar mandates
- buying small satellite positions that never move the needle, but still add complexity
The intent is reasonable: “I want to spread risk.”
The outcome is usually: “I’ve bought the same thing 6 times and paid extra for it.”
The mechanics: overlap + costs#
Two forces drive diworsification:
1) Overlap
If two funds hold mostly the same underlying assets, you haven’t diversified much. You’ve just split the same exposure into two wrappers.
2) Costs
Fees compound in the wrong direction.
- higher management fees
- more trading costs
- more tax drag (depending on structure)
You don’t need disaster for this to hurt you. A small fee difference over a long horizon is enough.
A simple test: “What risk does this reduce?”#
Before you add something new, ask:
- What risk does this reduce?
- What new risk does it introduce? (complexity is a risk)
- What does it cost? (fees, tax, attention)
If you can’t answer those cleanly, it’s usually noise.
Trade-off: fewer holdings can feel psychologically uncomfortable. That discomfort isn’t always a signal.
How to avoid it#
- Start with a small number of broad, low-cost building blocks
- Use satellites sparingly (and intentionally)
- Review overlap occasionally (not weekly)
- Keep your portfolio simple enough that you can maintain it
Most portfolios don’t fail because the chosen ETF was “wrong.” They fail because the system is too complex to stick with.