Those first times you realize you didn't think of smoking all day are your proof.
It begins for some in the 70's. It began for me in the 80's. For some later.
Yes it happens during the time most people give up.
Don't give up. Don't give in.
Those daye will become more frequent if you give it time.
I wasn't positive I was done until day 126. For some it takes longer.
But those days you forget are the beginning of your proof.
Look for them. Celebrate them.