You can use the practice bots in the practice room to build up muscle memory since they move predictably. I don't like using Ana bots and stuff because they don't move like humans, which messes up the prediction part.
To learn how to flick I straight up would just go flick bots for a bit when I had nothing better to do and I wanted to be on OW anyways. Then I would go into QP and try to flick things, fail miserably, repeat for awhile. Eventually I had the "aha" moment where I could consistently do that so I started to do it naturally.
Whether it be flicks, using your arm, tracking, lifting your wrist, etc. that's a decent way to go about it. Seriously though, that last one is where most people mess up.
I can fathom it cause I see it happen literally all the time. If you don't have ults that can wipe, yeah you gotta kill it. Most common team comps these days have those ults available to them, so they just build them up and dump em.
