It's just practice, really. Once you get a hang of it, it becomes easy. It's much easier than managing the work of a small team of 6 people. Or taking care of 6 dogs at the same time, for instance.

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Simple tasks like hunting and gathering were managed by our ancestors with ease, fueling their brains and bodies with nutrient-dense animal foods.
You should have said "it's like playing fetch with 6 dogs at once" then. But I still wouldn't believe you, because code review is much more like chess than fetch.