system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do colds have 'stages' and attack your nose and throat at different times?

 I would expect a cold to attack your whole body more or less at one.. instead you'll hear "first it was in my nose and I was congested, then I had a sore throat, then I had a runny nose, etc. I would think that the virus would be able to get to your nose and throat at relatively the same time.
gpt
The progression works kinda like this. You inhale the virus, it gets lodged in your nose let's say. It starts attacking and lysing cells, because that how it be. The body responds with inflammation and an increase in mucus production, which contains the active immune components. Your post nasal drip brings it down to your throat, which the virus then attacks and wreaks havoc. As luck would have it, a couple times when you breathe in you accidentally pull some of this post nasal drip / throat mucus into your lungs and voila, now you have an infection there. Since you usually swallow your post nasal drip, this can give you the vomiting and nausea component when your stomach fails to breakdown the viruses, which causes it to freak out and push the panic button, making you throw up. The change in symptoms from a stuffy nose to a runny nose is your body trying to fix it, and this leakage is what makes it mobile.

It can't attack systemically because it's not mobile enough. It's like living in a big city, if you don't have a means for transport you'll never leave the neighbourhood. For it to do that it would have to be in the blood stream, which is why when you get an attenuated vaccine you can get sick all at once. This isn't dangerous though because cold viruses target only the respiratory tract with a little bit of the digestive tract thrown in for free.