Even by his own admission ex-NASA engineer Mark Rober sucks at playing darts, but what he is good at is engineering, so rather that practice playing he did what he's good at and fixed the problem the proper way - by building a motion tracking dart board that makes sure he hits the bullseye every time he throws a dart.
The motion-tracking board took three years from concept to completion and uses six Vicon motion-tracking cameras and normal darts equipped with infrared reflectors in order for the board to hone in to complete the perfect throw. You'll also notice from the video that the reaction time of the board is also pretty impressive, taking just 200 milliseconds for it to predict were the dart is going to land and position the board accordingly. It's also capable of adjusting itself more than 100 times before the dart hits.
Sadly we don't think you'll be able to build one of these yourself, it did take a rocket scientist to build this one after all!. So in the meantime your best bet and making sure you hit the bullseye every time is to keep on practicing.