Only Risk What You Can Lose

This is the most repeated piece of financial advice in existence and almost nobody explains how to actually arrive at the number. So it gets nodded at and ignored, and then people find out what their real number was the hard way.

Here is how I think about it.

The condition that matters

The rule applies wherever you do not control the outcome.

That is the distinguishing feature. Not risk, exactly. Control.

When you own a business you run, you have levers. Revenue drops, you can cut, pivot, sell something, work harder. The outcome is partly yours.

When you are a limited partner in someone else deal, you have no levers. When you own shares in a public company, you have no levers. When you invest alongside a sponsor in a syndication, you have signed a document and now you wait. You are not running the company. You are not managing the property. You made one decision and then handed the steering wheel to someone else for several years.

In those positions, the entire question is how much of your life you are willing to attach to a decision you will not get to revisit.

What I have watched happen

The failure looks the same every time.

Someone gets comfortable. The last deal worked, the sponsor seems excellent, the returns have been what was promised. So the next position is larger. Then larger again, because why spread it thin across mediocre options when this one is clearly good.

Then something happens that nobody modeled. A partner dies or gets divorced. A market moves. Legislation changes the economics of the asset. The sponsor turns out to be better at raising money than operating.

And the person is not just down. They are damaged, because a number that should have been a bad year became a structural problem in their life.

Every one of them could describe the risk beforehand. They just had it sized wrong.

How to actually set the number

Forget percentages for a moment. The question is not mathematical, it is imaginative.

Picture the position going to zero. Not down forty percent. Gone entirely, and not returning. Then ask what specifically changes about your life.

If the answer is that you would be annoyed and it would set you back, that is a size you can live with.

If the answer involves the words have to, I would have to sell something, I would have to change where my kids go to school, I would have to take work I do not want, the position is too big. Cut it until the sentence stops containing that phrase.

This is more useful than any percentage rule, because it is calibrated to your actual life rather than to a number from a book. Two people with identical net worth have completely different capacities depending on their income stability, their obligations, and how well they sleep.

Two things people get wrong

Concentration feels like conviction. It is intoxicating to be sure, and sizing up feels like the natural expression of certainty. But conviction is about whether you are right. Position size is about what happens when you are wrong. They are separate decisions and people collapse them constantly.

You can be extremely confident and still keep the position small. That is not timidity. That is understanding that confidence has never once prevented an outcome.

The relevant number is not what you can afford today. It is what you can afford across every plausible version of the next five years. Today you have income and no emergencies. The size should survive the version where that is not true, because you are locking money into something you cannot easily exit.

Diversification, said honestly

Spreading across several positions is not about maximizing return. It usually reduces it.

What it does is make any single wrong decision survivable. And since the thing that ends people is not being wrong but being wrong large, that trade is worth making at almost any stage.

The version of this I actually use: no single passive position should be able to change my life if it goes to zero. If it can, I either take a smaller piece or I do not go in.

The part nobody says

There is real freedom in this, beyond the arithmetic.

When a position cannot hurt you, you stop watching it. You do not check it at midnight. You do not make emotional decisions to protect it. You do not stay in a bad partnership because you cannot afford to be right too late.

Being properly sized is what allows you to be patient, and patience is where nearly all the return in long-hold investing actually comes from. People who are over-sized get shaken out at exactly the wrong moment, not because their thesis was wrong but because they could not afford to wait for it.

Size the position so that waiting is easy. Then wait.

The rule

If you cannot control it, assume you might lose all of it, and choose an amount where that loss is a bad year rather than a different life.

Then put it out of your mind, which is the entire point.