I reckon we've all done that, especially before we learned not to. I learned decades ago, and my method is what I thought about before each shot. My question is for anyone who wouldn't mind revealing how they mastered the 'no flinch.' My method was/is a bit different from what experienced and great shooters do. I've heard it taught that we should learn to ignore the pan flash. I suppose that works very well after much practice. Quality, fast locks like Siler and Kibler lessen the need to deal with a delay, I know, but we can't always tell what might slow the process. Dull flint, flint not aligned, dirty flash hole.
Decades ago I flinched. So I practiced with a wooden flints. When I got to the point my sight picture didn't change while 'firing,' I started priming the pan and firing without a loaded gun. After mastering that (ignoring the flash,) I was good to go.
But now at advanced age, and shooting less often, my method is a tad different. Now, when aiming, even with a very fast lock, I've taught myself to EXPECT the flash, to know that the flash is all important and that once that occurs, it is over; that the gun will fire on it's own and that my sight alignment won't change. Mental procedures are incredibly difficult to explain, and I've not really said what my mindset is at that critical instant, but it works for me. I've said all that to ask, HOW DID OR DO YOU OVERCOME FLINCHING, before or during the firing process. This is likely the longest thread opening question ever asked.