How to Apply First Principles in Personal Finance Decisions?

哈喽，这个问题挺有意思的，我试着用大白话聊聊我的看法。所谓“第一性原理”听起来很玄乎，但说白了就是一句话：别管别人怎么说、怎么做，也别管“规矩”是什么，你得自己去想这件事最根本的样子是什么。

把它用到个人理财上，威力巨大。因为理财这事儿，充满了各种“经验之谈”、“社会共识”和营销话术，很容易把人带沟里。用第一性原理，就是让你穿过这些迷雾，看清钱的本质。

我举几个例子，你马上就明白了。

例子一：买房

传统的说法是啥？“租房就是帮房东还贷，钱都打水漂了”、“成家立业必须有套房，越早上车越好”。

我们用第一性原理来拆解一下：

“房子”的本质是什么？ 首先，它是一个“住的地方”，满足你的居住需求。其次，它是一个“资产”，价格会波动，有金融属性。
为了“住”，我需要付出什么？ 如果买房，我要付出首付、月供（利息+本金）、税费、物业费、维修费。如果租房，我付出的是租金。
作为“资产”，它带给我什么？ 可能是升值带来的收益，也可能是贬值带来的亏损。同时，它占用了我大量的现金流（月供），让我没法把这些钱投到别的地方去。

好了，现在我们从头开始思考。问题不再是“该不该买房”，而是： “为了解决我未来10年的居住问题，综合考虑‘买’和‘租’各自的全部成本（包括机会成本，也就是如果我不买房，把首付和月供的差额拿去投资，会赚/亏多少钱），以及我所在城市的房价趋势、我的工作稳定性，哪个方案对我来说更划算、风险更低？”

你看，这么一想，你就不会被“必须买房”的口号绑架了。你可能会发现，在你所在的城市，或者在你目前的人生阶段，租房+理财是远比买房更优的选择。反之，你也可能通过计算，确认了买房确实是当下最明智的决策。重点是，这个结论是你自己推导出来的，而不是听来的。

例子二：投资

传统的说法：“我二舅推荐的这只股票能涨停”、“鸡蛋不能放一个篮子里，得买十几只基金分散风险”。

用第一性原理来拆解：

“投资”的本质是什么？ 是用今天的钱，去购买未来能产生更多钱的“资产”。
“赚钱”的本质是什么？ 长期来看，是分享人类社会经济发展的红利。公司创造利润，经济增长，你的资产就跟着增值。
投资的成本是什么？ 手续费、管理费、税，还有你花费的时间和精力。

从头思考： “我作为一个普通人，最简单、最省心、成本最低地分享整个经济发展红利的方式是什么？”

答案几乎是唯一的：购买代表整个市场（比如沪深300、标普500）的指数基金。 它帮你把钱分散到几百家头部公司里，你不需要研究个股，交易成本和管理费也极低。这个结论不是哪个“大神”告诉你的，而是从投资最根本的逻辑里推导出来的。你自然就对那些“内幕消息”和复杂的投资组合免疫了。

例子三：买车

传统的说法：“男人必须有辆车”、“出门有车方便多了”。

用第一性原理拆解：

“车”的本质是什么？ 是一个把你从A点移动到B点的交通工具。
为了这个“移动”，我有哪些选择？ 步行、自行车、公交、地铁、打车、租车、买车。
买车的总成本是多少？ 远不止车价。还有保险、油费/电费、保养、维修、停车费、折旧（这是最大的成本！）。

从头思考： “根据我的实际出行需求（比如每天通勤、周末购物、偶尔长途），综合计算以上所有选项的‘总成本’（包括金钱和时间），哪个组合方案最适合我？”

你可能会发现，对一个在公共交通发达的大城市、不常出远门的人来说，“地铁+打车”的组合，一年下来花的钱可能还不到养一台最便宜的车成本的一半，而且还省去了找车位和堵车的烦恼。

总结一下：

在理财决策中运用第一性原理，不是让你变成一个精算师，天天抱着计算器。它是一种思维方式：

质疑一切“理所当然”：为什么一定要这么做？这是唯一的选择吗？
回归事物本质：这件事最核心的需求/目的是什么？
基于事实和逻辑，而不是情绪和传统，做出自己的判断。

当你习惯了这样思考，你会发现很多让你焦虑的理财问题，其实都有了清晰的答案。这个答案不一定和别人一样，但它一定是最适合你自己的。 Hello, this is an interesting question. I'll try to share my thoughts in plain language. The so-called "First Principles" might sound profound, but in essence, it boils down to one sentence: Don't mind what others say or do, and don't bother with what the "rules" are; you need to figure out what the most fundamental nature of something is for yourself.

Applying this to personal finance has immense power. That's because personal finance is full of "conventional wisdom," "social consensus," and marketing rhetoric, which can easily lead people astray. Using first principles allows you to cut through these fogs and see the true nature of money.

Let me give you a few examples, and you'll immediately understand.

Example 1: Buying a House

What's the traditional saying? "Renting is just helping your landlord pay off their mortgage, and your money goes down the drain," or "You must own a house to settle down and start a family; the sooner you get on the property ladder, the better."

Let's break it down using first principles:

What is the essence of a "house"? Firstly, it's a "place to live," fulfilling your housing needs. Secondly, it's an "asset" whose price can fluctuate, possessing financial attributes.
What do I need to pay for "living"? If I buy a house, I pay a down payment, monthly mortgage payments (interest + principal), taxes, property management fees, and maintenance costs. If I rent, I pay rent.
As an "asset," what does it bring me? It could be gains from appreciation or losses from depreciation. At the same time, it ties up a significant amount of my cash flow (monthly mortgage), preventing me from investing that money elsewhere.

Alright, now let's think from scratch. The question is no longer "should I buy a house," but rather: "To solve my housing problem for the next 10 years, considering the total costs of both 'buying' and 'renting' (including opportunity cost, i.e., how much I would gain/lose if I invested the difference between a down payment and monthly mortgage payments instead of buying), as well as the housing trends in my city and my job stability, which option is more cost-effective and lower risk for me?"

You see, thinking this way prevents you from being held hostage by the slogan "you must buy a house." You might find that, in your city or at your current stage of life, renting + investing is a far superior option to buying. Conversely, you might also confirm through calculation that buying a house is indeed the wisest decision right now. The key is that this conclusion is derived by you, not something you merely heard.

Example 2: Investing

Traditional sayings: "My second uncle recommended this stock, it's going to hit its daily limit," or "Don't put all your eggs in one basket; you need to buy a dozen funds to diversify risk."

Let's break it down using first principles:

What is the essence of "investing"? It's using today's money to buy "assets" that can generate more money in the future.
What is the essence of "making money"? In the long run, it's sharing in the dividends of human societal and economic development. Companies generate profits, economies grow, and your assets appreciate accordingly.
What are the costs of investing? Transaction fees, management fees, taxes, and the time and effort you spend.

Thinking from scratch: "As an ordinary person, what is the simplest, most worry-free, and lowest-cost way for me to share in the dividends of overall economic development?"

The answer is almost singular: Buy index funds that represent the entire market (such as CSI 300 or S&P 500). This helps you diversify your money across hundreds of leading companies; you don't need to research individual stocks, and transaction and management fees are extremely low. This conclusion isn't something a "guru" told you; it's derived from the most fundamental logic of investing. You naturally become immune to "insider tips" and complex investment portfolios.

Example 3: Buying a Car

Traditional sayings: "A man must own a car," or "It's much more convenient to have a car when you go out."

Let's break it down using first principles:

What is the essence of a "car"? It's a means of transportation that moves you from point A to point B.
For this "movement," what are my options? Walking, cycling, public bus, subway, ride-hailing, car rental, buying a car.
What is the total cost of buying a car? It's far more than just the purchase price. There's also insurance, fuel/electricity costs, maintenance, repairs, parking fees, and depreciation (which is the biggest cost!).

Thinking from scratch: "Based on my actual travel needs (e.g., daily commute, weekend shopping, occasional long-distance trips), and comprehensively calculating the 'total cost' (including money and time) of all the above options, which combination of solutions is most suitable for me?"

You might find that for someone living in a large city with developed public transport and who doesn't often travel far, the combination of "subway + ride-hailing" might cost less than half the annual expense of owning even the cheapest car, and it also saves you the hassle of finding parking and dealing with traffic jams.

To summarize:

Applying first principles to financial decisions isn't about turning you into an actuary who constantly crunches numbers. It's a way of thinking:

Question everything "taken for granted": Why must it be done this way? Is this the only option?
Return to the essence of things: What is the core need/purpose of this matter?
Make your own judgments based on facts and logic, not emotions or tradition.

Once you get used to thinking this way, you'll find that many financial problems that cause you anxiety actually have clear answers. This answer might not be the same as others', but it will certainly be the most suitable for you.