New Delhi, April 26 -- Here is a small experiment. Imagine two yellow lines drawn on a railway track, one closer to you, one farther away. Which one looks longer? Almost everyone says the farther one. But both lines are exactly the same length. What makes it truly unsettling is this: even after you know it is an illusion, you cannot unsee it. The brain keeps getting it wrong.

Investing in uncertain markets works the same way. Our instincts consistently mislead us at the moments that matter most. And just like the optical illusion, knowing about the bias is not enough. You need the investing equivalent of a ruler. You need frameworks.

Equities fall 10 to 20% in almost every calendar year. And yet, over the last 46 years, 37 of those year...