Yes, exactly this. If the whole of parenting could be boiled down to “just be firm a few times when they’re one” for all children all those parenting experts would be out of business pretty quickly!
Has anyone actually said that children's behaviour is magically sorted if you're firm a couple of times at one though?
Most people seem to fairly sensibly have a fairly middle of the road approach where as parents they teach their children appropriate behaviour over time, and this takes time and effort on the part of the parents.
It's a bit like any thread about child behaviour inevitably ends up with some arguing that people expect perfect behaviour in cafes (reality, almost nobody does and there's a huge difference between a child being a child and a parent allowing their children to run feral around the place).
Then there's arguments that either children run wild in public places or you have to give children tablets and screens to have anything resembling appropriate behaviour (again the entirely sensible middle ground of having age appropriate expectations, engaging children, supporting them to behave, teaching them expectations like all middle of the road parents do is conspicuously absent).
And if all else fails, simply pretend that parenting makes very little difference and some children pop out the womb naturally knowing what's acceptable behaviour.
Most children don't charge around shops helping themselves to various items as only putting them back on their terms. Most children don't run wild in cafes, restaurants and public spaces. It's not because they're born perfect, it's because their parents (who will probably all have slightly different parenting approaches) have chosen to make the effort.