The fantasy version of compartmentalization is clean. Work life over here, volunteer thing over there, the account where you post about model trains somewhere else entirely, and nothing crosses.
The real version is that I have leaked between compartments at least four times that I know about, and the count is only that low because I stopped keeping compartments I didn't need.
the walls are never the failure
People spend all their effort on the walls. Separate browser profile, separate email, separate device, maybe a VM. The walls are the easy part. You build them once and they mostly hold.
Things leak at the seams — the places where a human has to move between compartments and the friction is high enough that they start cutting corners.
the convenience seam
This is the big one. Not a technical failure. Fatigue.
You're in the wrong profile at 1am, the thing you need is one tab away in the other one, and you tell yourself it's fine just this once. It usually is fine. Then one time it isn't, because the site you loaded fingerprints you, or because you pasted from the wrong clipboard, or because you were signed in and didn't notice.
The fix isn't discipline. Discipline is a thing you run out of. The fix is making the right thing cheaper than the wrong thing: separate profiles that launch from separate icons, distinct visual themes so you can tell at a glance where you are, and an explicit rule that when you're too tired to know which window is which, you stop.
I keep persistent named browser profiles rather than juggling private windows, because private windows lose state and losing state is exactly what makes people cheat.
# named, persistent profiles — no shared cookie jar between them
firefox -P research --no-remote &
firefox -P admin --no-remote &
# create or inspect profiles
firefox --ProfileManager
The --no-remote matters more than it looks: without it a launch can get handed to an already-running instance and you end up in the wrong profile without any signal that it happened.
the identity seam
Compartments don't fail at the network layer nearly as often as they fail at the style layer.
Things I have personally seen tie two supposedly separate identities together:
- The same avatar, cropped differently. Reverse image search does not care about your crop.
- A handle that's a variation on another handle.
birchpathandbirch_pathare one identity. - Bio text copy-pasted verbatim between accounts, because writing a bio is annoying.
- A recovery phone number shared across both. This one is silent and total.
- The same three typos. I have a signature typo. I know what it is. I'm not telling you.
- Posting the same niche opinion about the same niche thing within an hour, twice.
Correlation doesn't need a smoking gun. It needs two weak signals that agree, and a person patient enough to notice they agree.
the device seam
One device, two compartments, and the device is quietly the third party in every conversation. Shared clipboard. Shared DNS. Shared keyboard dictionary that will autocomplete a name you only ever typed in the other context. Screenshot folders that sync to one cloud account. A notification from compartment A arriving on screen while you're recording a call in compartment B.
Phones are worse than laptops here, because phones aggressively unify things on your behalf and call it a feature.
the human seam
The one nobody plans for. You tell a friend about a thing you did in another compartment because you're proud of it, or because it's 2am and you're talking. Then they mention it to someone. This has nothing to do with your setup and everything to do with the fact that keeping something separate means genuinely not talking about it, and that's lonely in a way that people underestimate before they try it.
the cost is real and it's paid daily
Every compartment carries a running tax:
- Credentials, backup codes, and recovery paths, per compartment.
- Devices or profiles kept updated, per compartment.
- Context-switch overhead every single time.
- A social cost — the topics you can't raise, the introductions you can't make.
- A failure mode where you lose access to something because the recovery route lived in a compartment you burned.
That's why the honest advice is often fewer, better compartments. Two hard walls you maintain religiously beat six mushy ones you're constantly stepping over. Three is my practical ceiling. Past that I start making mistakes, and a compartment you violate regularly is worse than none — it's the same exposure plus false confidence.
when to just not
If your threat model says the adversary is opportunistic and automated, compartments buy you very little, and the effort is better spent on unique passwords, MFA, and updates.
Compartments are for when someone is looking at you, specifically: connecting the person to the account, the account to the source, the source to a place. That's when the wall earns its tax.
Otherwise you're just making your own life harder in a very tidy way that feels productive. Been there. Still catch myself doing it.