Properly positioned nail nicks, half stops on some knives, stainless integral liners-bolsters, and swedges...
Thats one of my bigest complaints. Both Karen and I have reached an age were we have some problems with the hands. Karen with the carpel tunnel thing she just had a series of surguries on, and mine from a life time of turning wrenches and machine handles as a machinist. I've handled pocket knives in stores that I could not open because the nail nick was too far back. A couple were back past the halfway point. No way for me to open without a pair of pliers. One reaches a stage in life when child proof caps also mean a senior citizen can't get in them either.
Half stops are nice but I can get by without if I have to, and the knife has a nail nick positioned properly and is smooth. That means internal parts polished like they used to in the old days so it pulls open smooth as butter.