Learn from my investing mistakes: 3 hard lessons every investor must learn

Every investor talks about their wins. Fewer talk honestly about their mistakes.

In this piece, I want to do the opposite.

I’ll share two investing decisions I made early in my journey—mistakes I didn’t just make once, but twice. They were painful at the time, but they shaped how I invest today. If you’re still building your portfolio, these lessons may save you years of frustration and missed upside.

Let’s start at the beginning.

My first big investing mistake: Selling DBS too early

Back in August 2011, I was still a university student. I bought 1,000 shares of DBS Group Holdings, one of Singapore’s largest banks, at S$13.50 per share. At that time, odd lots weren’t common, so buying 1,000 shares felt like a big deal. The total cost was about S$13,500, which was a huge sum for me back then.

Then Mr Market did what Mr Market does best.

By December, DBS had fallen to around S$11.50, putting me at an unrealised loss of roughly S$2,000 in just four months. As a full-time student and part-time tutor, that loss amounted to close to 100 hours of tutoring. It hurt.

But that wasn’t my mistake.

Within a couple of months, DBS recovered. By August 2012, the stock hit S$14.70, giving me about a 10% return in a year. Feeling proud and relieved, I sold my shares, locked in roughly S$1,000 of profit, and congratulated myself on a “good investment”.

In hindsight, that decision cost me far more than the earlier paper loss.

DBS continued to compound steadily as it expanded across Southeast Asia, Hong Kong, and China. By August 2013, it was trading at S$17.20, and by the end of 2014, around S$20.50. Had I held on, my return would have been close to 50%—not including dividends.

Source: Yahoo Finance

I sold not because the business deteriorated, but because the price went up.

And I didn’t learn my lesson.

Repeating the same mistake with Meta (Facebook)

Fast forward to mid-2014.

I bought Meta Platforms (then Facebook) at US$63 per share. Within a year, the stock surged to about US$96. Once again, I felt clever. I told myself it couldn’t possibly go much higher. I locked in my gains and walked away feeling accomplished.

You already know how this story ends.

Facebook went on to become one of the most dominant businesses of our generation. The stock continued to compound for years as its network effects, advertising dominance, and cash flows exploded.

This was when the lesson finally sank in.

I wasn’t selling because the business was overvalued or broken. I was selling because I was anchored to the stock price.

3 investing lessons I learned the hard way

You don’t have to repeat these mistakes. Here are three lessons that reshaped how I invest today.

1. A stock is ownership in a business, not a trading chip

When you buy a stock, you’re not buying a ticker symbol. You’re buying a slice of a real business.

The stock market is simply a platform that allows everyday investors to own exceptional companies. If you treat stocks as pieces of paper meant for quick profits, you’ll naturally sell too early. When you think like a business owner, patience becomes much easier.

This mindset shift alone can dramatically change your long-term returns.

2. Stock analysis is about business quality, not share price

One of the biggest traps investors fall into is judging a stock by how “high” or “low” its price looks.

A proper stock analysis goes far deeper. It looks at cash flows, growth runway, competitive advantages, and economic moat. These are the factors that drive intrinsic value over time—not yesterday’s price chart.

Both DBS and Meta continued to grow as businesses. The mistake wasn’t buying them. The mistake was ignoring their fundamentals once the price moved.

3. Knowing when to sell is more important than knowing when to buy

Long-term investing doesn’t mean buying and forgetting forever. It means buying with conviction and monitoring the business intelligently.

Today, I only sell under three conditions.

First, when the business suffers irreversible deterioration.

Second, when a clearly superior opportunity appears, capital needs to be reallocated.

Third, when my original investment thesis turns out to be wrong.

Notice what’s missing from this list: “The price has gone up.”

A final thought on Human Misjudgement

Charlie Munger captured these behaviours perfectly in The Psychology of Human Misjudgement. Many of the mistakes I made—fear, overconfidence, anchoring to price—are deeply human. The book is dense, but the lessons are invaluable.

That’s why I took the time to summarise and explain these ideas in simple, practical terms for investors who want to make better decisions without wading through a thick textbook.

If you want to learn how to avoid these behavioural traps and receive the concise guide, you can download it here.

Download it now

Because in investing, the biggest risks often aren’t market crashes—they’re the mistakes we repeat without realising it.