My daughter (really a guitar player) brings her mandolin to play when she visits ... as it's easier to transport on the plane and such. She loves to play Celtic and other music with me, but she has serious mandolin picking issues.
I watched her carefully as she picks, and I think she's one of those "freaks of nature" who doesn't rest their right hand on the upper side of the bridge while picking. She anchors her right picking hand with her pinkie and ring finger on the bottom edge of the bridge.
She can't hold a mandolin pick properly if her life depended on it. She said every teacher and fellow player has given her lessons, begged, bribed ... tried everything to instill good mandolin picking techniques. She's watched video after video with famous mandolin pickers offering their techniques ... to no avail.
So, being her Mom, I thought maybe she could work with her "pick style disability", rather than fight it .... so I suggested she get a thumb pick. The way her hand is positioned .... her thumb seems to be in the ideal position to pick away.
She's gifted with the ability to hear and play complex rhythms and tunes, but I pick far better with less talent because I have very good pick holding skills (I'm told).
Thanks for mandolin thumb picking advice and ideas!