Well... once you get a few fingers in and shes wet and enjoying it, most often its possible to slip in a few more and next thing you know you're halfway in already.
Those that enjoy it want you to fill them up, others that don't ask you to go back to using 1 or 2 fingers. Never had any issues, its all "in the moment" stuff...
Again...I must disagree. I need to answer this carefully so as to keep it generic & not advertising.
Fisting is an act that many women consider extreme & don't even allow their personal partner(s) to do. It really isn't a vanilla act, after all. Here's an experiment that you can try though, if you're still curious about 'just trying it'. Next time you're in your car, at a stoplight, just run a finger casually around the edge of your nostril. If the lights stay red long enough, dig a little deeper, do a little exploration just to see what happens.
Then, when the light turns green, jam your hand right in there...four fingers deep.
/smh
An sp 'permitting' you to do it once you are mid-session doesn't mean she's enjoying it. It means she isn't objecting to it by violently kicking you across the room, or stopping you by saying "No. Don't. This isn't something I am comfortable with." Consent, right?