The Kelly Criterion

The Kelly criterion is a
Very popularized mathematical formulation
Of a simple concept
And the simple concept is

[Chorus]
Don't risk everything
Stay outta jail
Don't risk everything
'Cause you could just lose everything
Don't risk everything
Avoid ruin
Don't risk everything
'Cause you could just lose everything

Don't bet everything on one big gamble
Just be very careful how much you bet each time
So you don't lose the whole kitty
The Kelly criterion mathematically formulates
If you're a gambler
Even when you have an edge
How much should you gamble per hand
Even when you have an edge, you can still lose
Let's say you have a 51-49 edge
Every gambler knows not to bet the whole kitty
On that 51-49 edge
You'd just lose everything
And you don't get to come back to the average

[Chorus]
Don't risk everything
Stay outta jail
Don't risk everything
'Cause you could just lose everything
Don't risk everything
Avoid ruin
Don't risk everything
'Cause you could just lose everything

Ergodicity, what is true
For a hundred people on average
Isn't the same as one person
Averaging that same thing a hundred times
The easiest way to see that
Is by playing Russian roulette
Six people play Russian roulette once each
Each winner gets a billion dollars
One person ends up dead
Five people have a billion dollars
Versus one person
Who plays Russian roulette
With the same one gun - six times
Is never gonna end up a billionaire
He's gonna end up worth zero

[Chorus]
Don't risk everything
Stay outta jail
Don't risk everything
'Cause you could just lose everything
Don't risk everything
Avoid ruin
Don't risk everything
'Cause you could just lose everything

And so, risk-taking
Especially when the averages
Are calculated across large populations
Is not always rational
The Kelly criterion helps you avoid
Ruin
The number-one way in which people get ruined
In modern business
Is not by betting too much
But it's by cutting corners
And doing unethical things
Or downright illegal things
Ending up in an orange jumpsuit in prison
Or having your reputation ruined
Is the same as getting wiped to zero
So never do those things
Never do those things

[Chorus]
Don't risk everything
Stay outta jail
Don't risk everything
'Cause you could just lose everything
Don't risk everything
Avoid ruin
Don't risk everything
'Cause you could just lose everything

[Chorus]
Don't risk everything
Stay outta jail
Don't risk everything
'Cause you could just lose everything
Don't risk everything
Avoid ruin
Don't risk everything
'Cause you could just lose everything