Quantum of Pain

When I was young my mother told me to listen carefully to what my body was telling me. Even though she was probably talking about eating too much candy, I am thinking about how it applies to running. I'm wondering exactly how closely I can listen to what my body is telling me.

This is the Wong Pain Scale, where 0 is "I'm feelin' fine" and 5 is "Oh dear, I seem to have accidentally cut off my hand with a chainsaw."

A 1 might be natural soreness after a long run, a 2 might mean it's time for an ice bath, and a 3 means you may have injured yourself. But what about the difference between a 1.1 and a 1.2? or a 1.25? If I feel a slight twinge in my IT band, isn't it better to hit that spot with the foam roller sooner, before it gets worse? If I can't tell the difference between a 1.1 and a 1.2 then I might not take corrective action until I hit a 1.5. An injury will be easier to reverse if caught early. Recently my left IT band went from 1.5 to the low 2s. I worked it for 5 minutes every half hour until it was down to a 0.5, which to me felt like a -3. Ahhhhhhhh.... Ready to run again! Since then I've watched it closely, giving attention to anything over a 1.0

So what is the smallest unit of detectable injury, my own quantum of pain?