Curious if anyone has experience with thumb sucking.. is it true it's super hard for a child to stop?

My son started when he was a baby, I introduced the soother instead and he stopped. I tossed the soother around 8 months and he never went back to anything like sucking his thumb.

My youngest (2 months) wont take a soother. She doesnt like them. Which is fine, but I've noticed the last few days when she wakes up from a nap I go in to get her and shes sucking her hand or thumb. I always figured "you can throw away a soother, but cant throw away a thumb🤣". I've heard of friends kids who suck their thumb for a lonnnnng time, even well past toddler years. And the comments people make about thumb sucking... is it really that bad? Should I keep trying to introduce the soother? Or just let her suck her thumb? Idk the only reason I used a soother with my son was because of all the comments people made to me about thumb sucking. He was thankfully super easy to get rid of the soother. So idk what to do lol