I hold my pencil "wrong" and I wish someone would have worked with me when I was little to correct it. I have tire out easily and have some arthritis in my middle finger due to my grip. I definitely watch how my kids are holding their pencils. You don't know when you are 7 years old how it will affect you later.
I'm a repentant (but not reformed) thumb tucker. 
Source: https://theanonymousot.com/2013/03/22/when-to-fix-a-pencil-grasp/
Thanxs @beriberi for replying. I was also taught wrong. I think that is why this is such an important part of teaching for me. I do the thumb wrap when I don't concentrate and focus on my pencil grip. When I decided to become a teacher I had to re-teach myself because I can't try to teach the children the correct pencil grip if I don't do it properly.