The Law of Three is how children thing something is normative after three times. It comes in various forms.
Consider the common scenario. Daddy flies 18-month old Junior up in the air on his feet and says, “Whooo! Look at Junior! He’s an airplane! REARAARRWAAA…” Junior squeals with delight. “Again, again!” he cries. “Ok,” agrees Daddy. “Up, up again! Look at Junior! REAARARARAWAAA…” “Fly, Daddy, fly!” says Junior when he’s back down on the ground.
At this point, Daddy has a very important decision to make. If he flies Junior again, for the third time, it is going to become astronomically harder to quit after that. Junior’s feelings will be hurt if he quits now, but they will be hurt unreasonably more after that third time. I don’t know why it is, it just is. Try it.
Another common scenario is when you’re eating ice cream. You get your little bowl and walk past your preschooler finishing her nuggets and carrots. Feeling generous, you ask, “Want a bite?” and hold out the spoon. Thrilled, Sarah takes the bite and says in response, “I like ice cream, Mom.” Wanting to be a good sport (after all, you have to model sharing in order to expect it), you say, “You do? Ok, here’s one more!” Gleeful at her score, Sarah takes the second bite off the spoon. “I like it, Mom.” she repeats, wiping her mouth. “I like it.” You are now at decision point like Daddy was above. If you say now, “Sorry sweetie. No more…” Sarah is going to be upset. Clearly her dinner is not as exciting as her treat and she will probably pout and stare at her plate for awhile. But if you say, “Ok one more, and then you finish your dinner,” there will be a special victory she has won. She will feel more entitled than she would have had you stopped at two bites. She will feel more inclined to your food, your dessert, ice cream, or getting what she wants. She will be more likely to ask, beg, or whine. I have no idea why this is the case, but it is. Test it.
The last common scenario I can think of off the top of my head is the ol’ grandparents visit. If Grandma and Granddad come over with a suitcase of toys once, the kids will see it as a wonderful surprise. They may raise their eyebrows when they come over a second time, but they will not expect them to bless them again like that. If they do it again that second time, the kids will eagerly await Grandma and Granddad’s visit the third time, expecting that suitcase. If Grandma and Granddad decline at that second point, they will disappoint their grandchildren for sure. But if Grandma and Granddad bring the suitcase of blessing the third time, they will confirm their grandchildren’s sense of lawfulness and it will be expected that whenever they show up, they will indeed bring toys. Be sure that the spoiled child syndrome will raise its ugly head if/when Grandma and Granddad forget that suitcase in the future.
So you see what I mean. The same goes for other treats or perks that children encounter. There is something magical in the psychology of a small child’s brain that cements an expectation after three trials. Try this with an older infant and a cookie “hidden” somewhere nearby and you’ll see it forming in action.
Now of course the Law of Three can work for you, too. That is the key. After your child learns something exactly the same way three times, they start to really internalize it. With the exception of toilet training or something complex like that which needs multiple trials again and again, kids can pick up most things after three trials. Or if they don’t, you can at least be sure that they have formed a memory of what they should be doing, even if they can’t ideally do it all the time. So, try this out in the area of how to play with a toy, come when you call, share with a sibling, clean up their room, tell you they have a note in their backpack for you, take their shoes off when they come in the house, or whatever other thing you want them to handle on their own. Run the scenario multiple times, and do the same thing the same way until they exhibit the right response three times in a row, and you can be confident that they at least know what they should be doing. You can then feel ok when they need correction later—but don’t nag or correct unless you’ve done your part first.