One usually, my thumb but I can do a forefinger alone or a two finger grip. I find it easy to do with one thumb and I am perplexed by the word struggle. On the other hand I have to focus to flip a knife open. Enough that I’m not much of a fan of the flipper as an opening method.
Smock, Baby Jess Horn CE, Spydiechef, Schempp Bowie,Ti Fluted Military, Titanium Military, Native S30 V and G10, PM 2 in S35VN, and S110V, Manix 2 LW BD1, Sage 5, Positron black CPM S30V, Chaparral w/Raffir Noble scales, SuperLeaf VG 10, Ladybug H1, Dragonfly 2 in ZDP 189 and Superblue/420J1 and H1, Delica in ZDP 189, Clipitool Standard, the Cook’s knife VG10, Santorum, paring and utility knives, all in MBS 26.