I remember the early years when I was taught CPR, the rules was if the heart was stopped, to start with three strikes to the chest, then check again.
I believe the thought at the time was that if the heart hadn't actually stopped but was in fibrillation this might be enough to break the heart out of it, either to get beating again or stop completely so it wasn't actively counteracting the subsequent pumping.
This changed so this shouldn't be done, possibly to prevent perforated lungs after adrenalin-boosted blows by a near panicking helper
I haven't kept my training current, so I'm still at the 15:2 which I expect is still considered better that hand-wringing bystanderism
Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain