Auk1124: No I would no longer say "I hate this when it happens"!
I now say, in instances like this, "that was my fault - concentrate - sight alignment, trigger control (squeeze - don't jerk!). And then commit to not failing in my efforts on the next grouping".
For the first 2 decades of my quest to attain accuracy and develop very accurate handloads I would indeed bemoan and hate it when a "flier" would spoil an otherwise notably good grouping (I fire 5 shot groupings for the very most part).
And for those 2 decades my loading room and powder storage locker were only festooned with my best (smallest!) targets (groupings with NO fliers).
BUT.... that did not seem to improve upon my occurrences of one shot fliers "spoiling" my groups.
SO.... for the last 3 decades I only tape up my groupings which show a single "flier" that has spoiled that otherwise good (great) grouping.
I have about 40 of these "spoiler" type targets on my powder storage lockers double doors!
I head each one "Famous Fliers I Have Shot" and clearly denote the "spoiled" group size and along with the groups size without the flier.
This constant reminder to me (every time I go for powder and/or primers) seems to be working for me - I now have a lower "percentage" of one shot fliers in my five shot groupings.
YOU are human - you made a human error of some type to send that bullet that far out of the grouping.
I think you will do better next time out (think positive).
Best of luck to you in your load development.
Hold into the wind
VarmintGuy