I'm not sure I agree with that statement. One shot, the first shot is the most important.
Shooting groups is fun, but the first shot out of the barrel is the most critical.
You can of course get the best of both theories.
Set up a target and leave it up. Go out in the morning, shoot one bullet. Then midday shoot another, a third late afternoon.
Next day, on the same target repeat the process. Do this for 3-4 days. Check the group and move it if necessary then repeat.
You get your multi-round group, yet each shot is the critical first shot.
I don't know of any matches you shoot one shot a day. Hunting if you do your job yes.
What is relevant is all the shots, good bad or anything.
Also each day is different temp, hold, you, etc.
I think that gets too deep into philosophical and ignores other factors.
At an extreme one day I can shoot at 45, the next day it can be -20.