Why are colds like
One Nostril: I’m cool
Other Nostril: They have taken the bridge and the second hall. We have barred the gates but cannot hold them for long. The ground shakes, drums… drums in the deep. We cannot get out. A shadow lurks in the dark. We can not get out… they are coming.
Because the duplication of nostrils, like the duplication of other critical parts like lungs and kidneys, raises the likelihood that even if one has its capacity degraded the other one still works. Oxygen intake is so critical and vulnerable we can mouth-breathe too, but this is literally the point.
this is the nasal cycle - each nostril alternates partially congesting itself. (exactly why they do this? less obvious.) however, this isn’t noticeable when your nose is otherwise in good order.
but if you throw in a little exogenous congestion, partially congested becomes completely congested and you find yourself alternately being able to breathe thru whichever nostril is in the decongested phase of the nasal cycle.