I really can't do any handsewing without one on my middle finger of right hand. The only sewing my Mom taught me was how to darn my dad's socks, and was taught to use a thimble then, probably when I was 12.
I have long fingernails (my own, not fakes), and I have to keep that one trimmed somewhat, or my thimble keeps slipping off. I also lick that finger before putting thimble on, and it stays put better.