I can get 3 fingers in easily. But I have a friend who can get her whole hand inside herself and she tells me that when a man or woman fucks her with their full fist it is an orgasm that can't be described.

I feel sad with my 3 fingers.

Any advice or insights?

keep trying!!!!

Do NOT keep trying. What is the point to putting a fist inside?

I have been with a few where I felt I could get my fist inside but never tried.

Besides fists vary in size so what would be the point?

Its a bit hard to imagine that any gal who has yet to give birth could insert even a small wrist.

do everything that feels good

Lesbian couples often progress to fisting and enjoy the emotions attached to stretching the vulva open very wide.
There is an element of B/D or S/M in some cases, a kind of power trip.

I fist my wife all the time. You just need to keep working it. Each time tryy to stretch it out a bit more. You will eventually get there. Don't rush it or you will just hurt yourself. My wife absolutely loves it she has at least one orgasm everytime, usually she'll have multiple orgasms. I love doing it to her to, I can't explain why, it just makes me feel so close to her. I never thought I would feel like that until I did it.

Why not go the next step and open it up wide enough to get your whole head up inside her.

I'm working on it

lol