How do you REALLY differentiate primal brain from prefrontal thoughts?

I had a task for 4pm – Go to the plant store and get your plants checked out.
My plants have stopped growing and I wanted to have an expert them out. I had this this task postponed for a while.
This time I was committed, the minute it was 4pm, I took my plants, car keys and headed out. But then I realized it was raining heavily.
I dropped my plan and came inside my house with the reasons –
It’s not really important to go now in the rain.
Don’t be unreasonable and do it for the sake of sticking to calendar

At that moment , those thoughts sounded like coming from my prefrontal cortex. It made total sense. In retrospect it seems like I wanted to avoid the discomfort of walking in the rain, but also my brain seemed to have my best interest (don’t go in the rain, do it when it’s sunny)
How do I know which brain gave me thoughts