After this discussion, I think there’s more nuance to it than that. 

If a process is low entropy but unknown it may essentially be as if it were high entropy. 

The intuition for that is that the number of unknown low entropy processes is sufficiently vast that the output is unguessable. 

There is still increased vulnerability, but it comes from the possibility of someone else discovering the same process.

Undisciplined

What I don't have good intuition for is why low entropy would always imply high predictability.

Low entropy -> high predictability -> increased vulnerability to brute force attack.

math

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[ELI5] How does low entropy hurt security?

> What I don't have good intuition for is why low entropy would always imply high predictability.

That's my understanding too:
Low entropy -> high predictability -> increased vulnerability to brute force attack.