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Here's the line I hear all the time: "But I only spent one day on it." Sure. You spent one day of effort. That doesn't mean it took one day.

That's the trap. Active time — the hours you actually had your hands on the work — and elapsed time — how long it took to land in someone's hands — are two completely different numbers. And when you juggle four things at once, that gap gets ugly fast.

Four items, one day of effort each, all started together. None of them is done until day four. Same person, same total work — but every single thing waited while you ping-ponged between the others. At four-at-once, each item spends most of its life sitting idle.

Now do them one at a time instead. Same total work, same end date — but your first delivery shows up on day one instead of day four. You only changed the order.

And that's before anyone mentions the cost of context switching. The full walkthrough — with the math drawn out — is in the video.