Thumb sucking is the worst. Even when they are convinced to actively try to stop it still happens in their sleep and the nail polish is useless in my experience. Just leads to a kid spitting in the corner. Ultimately leads to a thumb sucking prevention device and expanders costing thousands of dollars to correct over the course of a year or two. My second son had a pacifier because I was able to assist meaningfully in weaning him off of that. I was not permitted to chop off my first sons pacifier.