Why does first principles thinking necessitate students to continually question, 'Why is this definition valid?'

Haha, that's an interesting question. Let me try to share my thoughts in plain language.

When we were in school, teachers often used to say: "Memorize this definition; it will be on the exam." So, we'd just rote-memorize it, and few would ever think about where this definition came from, or why it was this way and not another. This is essentially a form of "intellectual laziness," where we simply accept the conclusions given to us by others.

First principles thinking, however, is about combating this laziness. It forces you to be like a curious child, constantly asking "why."

Let me give you an analogy.

Imagine you're learning to build a house. There are two ways to approach it:

1. Learning by Analogy: Your master tells you that load-bearing walls should be 30 centimeters thick, foundations should be dug 1 meter deep, and windows should be a certain size. You remember these rules, follow them, and the house you build turns out quite sturdy. But what if, one day, you're asked to build in an area with very soft soil, or using a completely new material? You'd be stumped, because your master never taught you that. You only know "how to do it," not "why it's done that way."

2. First Principles Thinking: You don't just learn how to build; you also ask: "Why should a load-bearing wall be 30 centimeters thick?" This question forces you to understand more fundamental things, such as: the load-bearing limit of bricks, the grade of cement, the height of the floors, gravity, wind forces, seismic requirements, and so on. Once you grasp this most fundamental, irreducible knowledge (like laws of physics, material science), you no longer rely on the ready-made "definition" or "rule" of "30 centimeters thick."

At this point, even if you were asked to build a house on the moon using carbon fiber, though you've never done it before, you could still start from the most basic principles (lunar gravity, vacuum environment, material properties) and derive a completely new construction plan yourself.

Returning to your question: Why bother asking "why is this definition valid?"

Because many so-called "definitions" are actually like that "30-centimeter-thick wall"—they are merely "conclusions" or "rules" that have been packaged and simplified from a bunch of underlying principles, under specific conditions, for ease of understanding and application.

When you question why it's valid, you're performing an "unpacking" action. You're opening up this canned knowledge to see what its original ingredients truly are. This process will allow you to:

• Truly understand, not just memorize: Knowledge is no longer isolated "Definition A" or "Formula B," but a network connected by underlying logic.
• Gain the ability to transfer and innovate: When you master the most fundamental logic, you can apply it to different fields and new problems, drawing inferences from one instance and even creating new methods that no one has thought of before. Because what you hold in your hand isn't a fixed recipe, but the ingredients and cooking principles.
• See through to the essence of things: It helps you filter out a lot of noise and superficialities, directly grasping the core. For example, with a business model, you don't need to care how many new concepts it's packaged with; if you break it down using first principles, you'll eventually find its essence might just be "buy low, sell high" or "monetizing information asymmetry."

So, constantly asking "why" isn't about splitting hairs; it's about breaking through the superficiality of knowledge and reaching its hardest core. It's a "tiring" but highly rewarding way of thinking.