"They'll make a mess"

They will. The cereal will go on the floor. The toast will be buttered on the plate and then on the table. The bag will be packed with the wrong book and a sock. The mess is real and the belief is accurate, and I'm not going to tell you it isn't a cost.

What I'd ask is what the mess is the cost of. It isn't the cost of the child being careless. It's the cost of the slow version, the same way the margin is, and it's paid for the same fortnight. A child who pours cereal for two weeks pours it onto the floor for about six days, onto the table for about four, and into the bowl after that, and those are my guesses and not a finding, but the shape is right. The mess is front-loaded. The takeover keeps the mess at zero and keeps the pouring at zero too.

There's also a second job hiding in the first. The cereal on the floor is a job, and it's a job a four-year-old can do badly, with a cloth and a lot of enthusiasm. The takeover usually takes both jobs, the pouring and the wiping, because you've got the cloth in your hand already. If the child pours and the child wipes, you've given away two things, and the second one is arguably the more useful. Most of adult life is clearing up after yourself.

I'd also gently ask what standard the mess is being measured against. A kitchen after a nine-year-old has made a sandwich is worse than a kitchen after you have. It's not worse than a kitchen after a meal. It's a few crumbs and a knife, and the reason it looks like a lot is that it's a mess you didn't make, and other people's mess always looks bigger.

The honest version of the objection is that you haven't got time for the mess on top of the margin, and that's fair, and chapter 21 is about finding the time. But I'd notice that the mess objection tends to get applied to the jobs that are messy and then quietly extended to the jobs that aren't. Doing a zip makes no mess. Packing a bag makes no mess. Filling in a form makes no mess. If the mess were the reason, those three would have gone to the child years ago.