Resolved Post Process Volume's Bloom: Why is the plane glowing?

So while I was testing glowing effects in Unity, I noticed that, while I can make things glow, I can't make only one GameObject glow in the scene. Whenever I make something glow, everything else also goes shiny. It's weird, because I only gave the "Post-process Volume" Component to the GameObject that I wanted to be shined and also gave it an exclusive layer.
Here is what I did:
1 - I created two gameObjects: "Plane" and "Pill".
2 - Added the "Post-process Layer" Component to the "Main Camera", making sure that only GameObjects layered as "Glow" would be targeted.
3 - Created two materials: "LimeGreen_mat" and "Lazer_mat". Both had emission turned on, but turning one of them off didn't change the outcome.
4 - Gave "Post-process Volume" Component to "Pill", added Bloom Override and marked "Is Global" because without it, nothing glows.
5 - Layered only the "Pill" as "Glow".

Whenever I raise or lower "Pill's Bloom intensity, everything else on the scene (in this case, the plane) also changes alongside with it. Why?

Images:

What I did:


How the scene looks like (notice that only the pill has a profile icon attached to it):

 

That is how Post-Processing works - it's applying a process, to the whole screen, after you have rendered every object (and at a stage where the pipeline does not know anything about individual objects).

To make individual objects glow (while some others don't), the objects you want need to be brighter (so, emission is usually a good way to do this) than the other objects, and you also need to set a threshold on your bloom so that it only affects the brightest objects in the scene.

 

Thank you so much for the explanation, I got it now!