The investing internet is full of people who bought the index in 2010, held on, and now explain how disciplined they are. Discipline is easy in a bull market. It's the mistakes that show you who you actually are as an investor.
I've made all ten of these. Some more than once. None of them were exotic. That's the point. The decisions that hurt me weren't clever derivatives blowing up, they were the ordinary, human, completely avoidable ones. Read them as a checklist of what not to do.
1. Waiting for the perfect time to buy#
For years I treated investing like catching a train. I'd watch the market, decide it was "too high," and wait for the pullback that would let me get in at a better price. Sometimes the pullback came and I still didn't buy, because by then I was waiting for it to go lower. Most of the time it just kept climbing without me.
Sitting in cash waiting for a better entry is one of the most expensive habits in investing. The money you keep on the sidelines earns nothing while the market compounds without you. And the cruel part is that even when you're right about the dip, you usually freeze and miss it anyway.
The fix: decide on an amount, pick a date every month, and buy regardless of the headlines. Time in the market beats timing the market, and it isn't close. If a lump sum scares you, spread it over a few months and then stop overthinking it.
2. Betting big on stocks I was sure about#
Early on I confused conviction with edge. I'd read everything about a company, become convinced, and put a large slice of my portfolio into a single name. When I was right it felt like genius. When I was wrong, and I was wrong plenty, one position could undo a year of careful saving.
A single stock can go to zero for reasons that have nothing to do with how well you did your homework. Fraud, regulation, a better competitor, a currency you didn't think about. No amount of research removes that risk, because the risk isn't about being smart, it's about being concentrated.
The fix: build your core out of broad index funds and treat individual stock picking as a small satellite, if you do it at all. Five percent of your portfolio in a name you love won't sink you. Thirty percent will.
3. Panic selling at the bottom#
The worst trade of my life was selling good assets in the middle of a crash because I couldn't stand watching the number fall. I told myself I was "protecting capital." What I was actually doing was locking in a loss and handing my shares to someone calmer than me. The market recovered. My sold-off position did not come back to me.
Selling in a drawdown turns a temporary, on-paper loss into a permanent, realised one. The market spends most of its life climbing, but it pays for that climb with sharp, frightening drops. If you sell every time it gets scary, you only ever capture the pain and never the recovery.
The fix: write your plan down while you're calm, then automate as much as you can so you're not making decisions during the panic. Hold enough cash and bonds that you're never forced to sell equities at the worst moment. If you tend to react, stop checking the portfolio during a sell-off.
4. Chasing whatever just went up#
I've bought the fund that topped the performance table last year. I've piled into the sector everyone was talking about right as it peaked. Performance chasing feels like momentum and smart positioning. It's almost always buying high after the easy gains are gone.
Last year's winner is rarely next year's winner. By the time a fund or a theme is on every front page, the returns that made it famous are already in the rearview mirror, and you're buying the hype, not the future. You end up with a portfolio that's a museum of yesterday's good ideas.
The fix: choose a sensible, boring allocation and ignore the leaderboard entirely. A global index fund quietly owns the next winner before anyone knows it's the winner. You don't have to chase what you already own.
5. Ignoring costs, fees, and fund structure#
For a long time I paid almost no attention to what my investing actually cost. High expense ratios, expensive actively managed funds, and as a non-US person, the wrong fund domicile. Every one of those is a small leak, and small leaks sink the ship over thirty years.
A one percent annual fee sounds trivial. Over an investing lifetime it can quietly eat a third of your final wealth. For expats it gets worse: hold the wrong ETFs as a non-US person and you can face higher dividend withholding and estate tax exposure you never needed to take on, on top of the currency conversion costs nobody warns you about.
The fix: keep costs ruthlessly low with broad index funds. If you're a non-US person, use Irish-domiciled UCITS ETFs rather than US-domiciled ones, and understand the withholding and estate rules before you buy. I went deep on the expat side of this in the Expat FI Playbook.
6. Tinkering with a portfolio that was already fine#
There was a stretch where I treated my portfolio like a garden that needed constant pruning. A trade here, a tweak there, a new fund I'd read about. It felt productive. It was the opposite. Every transaction had a cost, a spread, and a chance to be wrong, and all that activity added up to worse returns than if I'd simply done nothing.
Activity is not the same as progress. The portfolio that gets left alone usually beats the one that's constantly "optimised," because the tinkering introduces costs and emotional decisions while the underlying businesses just keep compounding on their own.
The fix: set a target allocation, rebalance on a fixed rule once or twice a year, and otherwise leave it alone. Boring is a feature. The best thing you can do most days is nothing.
7. Treating options like lottery tickets#
When I first touched options, I used them the way most people do: buying cheap out-of-the-money calls and puts, hoping for a big payoff. It's exciting. It's also a slow way to give your money away. Most of those bets expire worthless, and the few that pay rarely make up for the steady bleed.
Buying options is buying hope with an expiry date. Time works against you on every single position. The people who make options a real income stream are almost always on the other side of that trade, selling the premium that the hopeful buyers keep handing over.
The fix: if you trade options at all, sell premium systematically on quality names you'd be happy to own, size it carefully, and follow a written plan through the bad weeks. Never buy a lottery ticket and call it investing. I treat the active lane as a disciplined income business, not a casino.
8. Holding too much idle cash, in the wrong currency#
This one is specific to the globally mobile, and it cost me more than I'd like to admit. I let large cash balances sit for years, often in my earning currency, telling myself I was being prudent. Meanwhile inflation chipped away at it and the currency drifted against the places I actually planned to spend.
For an expat, cash isn't just exposed to inflation, it's exposed to currency risk on top. Holding years of savings in a currency you'll never retire in is a silent, grinding loss you don't notice until you convert it. Prudence and procrastination look identical right up until the exchange rate moves.
The fix: keep a deliberate cash buffer for emergencies and near-term spending, and invest the rest on a schedule. If you know your retirement currency, start tilting toward assets that match it well before you need them. Don't let "safe" cash quietly lose a third of its purchasing power.
9. Investing money I was going to need soon#
I once put money into the market that I needed within the year, reaching for a little extra return. Then life happened, the timing was bad, and I had to sell at a loss to free up the cash. That's the worst possible reason to sell: not because you chose to, but because you had no choice.
Money you'll need in the next couple of years has no business being in volatile assets. The market doesn't care about your timeline. If you're forced to sell during a downturn to cover a real expense, you convert a paper dip into a permanent loss, and you do it at the worst possible moment.
The fix: keep a proper emergency fund and short-term reserve in cash or near-cash, separate from your investments. Only invest money you can leave alone for at least five years, ideally longer. The buffer isn't dead money, it's what lets the rest of your portfolio survive a bad year untouched.
10. Waiting until I "understood everything" to start#
The most expensive mistake on this list isn't a trade. It's the years I spent reading, researching, and waiting until I felt ready, while my money sat doing nothing. I wanted to understand every tax rule, every fund, every scenario before I committed a single dollar. By the time I felt "ready," I'd already lost years of compounding I'll never get back.
You will never understand everything. The rules change, the products change, and your situation changes. The cost of waiting for perfect knowledge is almost always larger than the cost of starting with good-enough knowledge and improving as you go. Compounding rewards the years you're invested, not the years you spent preparing to invest.
The fix: start now with something simple and sensible, a low-cost global index fund and a regular contribution, then refine as you learn. A decent plan you actually follow beats a perfect plan you're still researching. The best day to start was years ago. The second best day is today.
The thread running through all ten#
Look back at the list and you'll notice none of these were about being smart enough. They were about behaviour. Patience, discipline, knowing what I needed and when, and getting out of my own way. The market doesn't punish people for being uninformed nearly as often as it punishes them for being impatient, fearful, or restless.
If you take one thing from my expensive education, take this: a simple plan, followed consistently for a long time, beats almost everything clever you could try instead. Buy broadly, keep costs low, hold a buffer so you're never forced to sell, mind your currencies if you live across borders, and then let time do the work it's very good at.
I paid for these lessons the slow way. You don't have to.
