Just looking from a high level at the task of holding a wafer-than disc steady between one's thumb and forefinger while strumming away for a number of minutes on a guitar appears somewhat difficult (maybe that's why Cheap Trick's Rick Nielsen is constantly flipping picks out to the audience . . .). For me, some days are easier than others and seem to be related to perhaps a higher surface moisture content of the two affected digits. I've tried picks with the little bumps on them and others with nice horizontal lines but haven't found these to be as good as the plain smooth picks (the kind that are often included in the little drawer of the case with the purchase of a new guitar . . .), though even these always require a bit of added "water" several times a session in order to not have to finish a song with an upside down pick.

If this used to be you and you've since found a solution, I'd be interested in learning what it is or if you've never struggled with this, I guess it would still be good to have your input in the forum.