"Spare the rod, spoil the child" - is the biggest bunch of BS ever written.
So, you have a 5 year old little girl/boy that is having a temper tantrum. She/he is having a knock down, screaming meemie fit. And you are pissed. In fact you are angry enough to want to throttle her/him. Of course you won't, because you are a civilized person and that is going too far.
But you are still madder than hell and you want your once of flesh.
But, how mad are you and what level of physical punishment will you administer? Enough, by God, to show this kid you won't put up with that kind of behavior - right? Well, how much is enough? And, what do you beat on the kid with - hand, switch, paddle with holes in it (which leaves blood blisters, by the way - bad ones), leather straps of various lengths and widths, RODS? Now, how much leverage and torque will you apply and to what part of the childs anatomy - in order to insure you get your point home? Are you that precise with the level of energy and do you have pin point accuracy of the application? Or do you even care?
The point being that the kid learns that his bad behavior will bring down hell, fire and brimstone and PAIN and that the kids parent, the one the child loves, looks up to and depends on, will metamorph into a scary engine of fear and pain.
So, the teaching mechanism becomes fear - not of the punishment, but fear of the parent turning into a monster. A child cannot separate the two, you see.
No, we have to believe we are more intelligent and mature than a child and we have humane ways to administer corrective discipline. We make sure the child understands that the inmates will not run the asylum and there are rules and BOTH PARENTS have to be on the same page in maintaining the rules.
For the childs sake. Believe it or not, the child wants this and will love you for it.