See time-to-live (TTL) packet
Plastic
The condensation of the nuclei
Veins contain valves preventing blood from circulating backwards.
It could be the radiator is clogged. The thermostat could be bad (prevents the coolant from circulating from radiator to engine block)
So we don't look like fools continuously staring into space without blinking. It also prevents tearing of the eyes.
The first amendment prevents the prior restraint of information. The first amendment gives people the freedom of speech and religion.
Choriod
Foam contains pockets of trapped air which prevents conduction.
Logging out of a computer has many benefits. It prevents others from using a laptop they should not be using, and prevents others from accessing information that is private.
Tumor/Cancer cells replicate uncontrollably because a mutation in their DNA prevents them from initiating Apoptosis, which would kill a damaged or old cell.
There is no limit and no database that tracks this information and prevents it.
Enyption