Diversification: Your Investment Portfolio's Best Insurance Policy

And how to do it right, from beginner to expert

I've been thinking a lot lately about conversations I have with newer investors. There's almost always this moment—usually after they've watched their first stock pick crater 30% in a week—when they ask me: "How do I make sure this never happens again?"

The answer isn't what they expect. It's not about finding the "perfect" stock or timing the market. It…