I suck my thumb out of habit and to feel good, familiar like a posture. I suck while driving my car, when going to sleep, when watching a movie. I put pressure on my front teeth so that's why they're bucked but I don't care because my mouth feels very comfortable the way it is. I sometimes suck and sometimes just rest my thumb on my bottom teeth, probably why I have a huge thumb callus.
I let others suck my thumb and have even sucked other thumbs, other than my own. I just love it I guess and, no, I don't ever want to give up. I couldn't anyway.