The author's first idea: risk and return are inseparable. If you want higher returns, you have to accept bigger swings and the chance of losses; anything claiming high returns with low risk is usually a problem.

He also explains why to diversify: no one can predict which market or stock will do best, so holding many assets reduces any single risk. And he explains that long-term stock returns come mostly from dividends and business growth, and that when valuations are high, future returns tend to be lower.

The author looks back over centuries of financial history: canals, railways, electricity and the internet all set off investment manias that ended with bubbles bursting. He also describes major crises such as the Great Depression, the stagflation of the 1970s, the dot-com bubble of 2000 and the 2008 financial crisis.

His message: markets go mad from time to time, and crashes and long slumps can happen again. Knowing history keeps you from panicking in the next crisis.

The author lists the human tendencies that most often lead investors astray, for example:

• Craving stories: we naturally prefer exciting stories to cold data, so we're easily drawn to hot themes.
• Overconfidence: believing we can pick winning stocks or time the market.
• Loss aversion: the pain of a loss is far greater than the joy of an equal gain, which makes people panic-sell in a crash.

His advice: admit you will make mistakes, set your rules in advance, and check prices and trade less.

The author says plainly that the interests of many financial firms don't line up with investors': brokers make money from trades, fund companies from management fees, and financial media from grabbing attention. High-fee products erode returns heavily over time.

He advises investors to stay away from high-cost products and frequent trading, and to favor low-cost, diversified index funds.

After the four pillars, the author explains how to actually allocate assets:

• First decide the split between stocks and safe assets (such as short-term government bonds); this is the most important decision.
• The new edition stresses dividing assets into two parts: a Liability Matching Portfolio (safe assets) that secures what you'll need to live on, and a Risk Portfolio that aims for growth.
• Within stocks, diversify across countries and types.
• Rebalance regularly, keeping your discipline when markets surge or crash.

The second edition adds developments from the past twenty years: the low-interest-rate era, the 2008 financial crisis and the 2020 pandemic crash, changes in various investment factor premiums, and new crazes such as crypto assets. The new Taiwanese edition organizes the content into “four keys and eighteen essential lessons.” The core ideas haven't changed: understand risk, remember history, manage your psychology, and keep costs low.

(This book presents investment ideas, not individual investment advice.)