Scaffolding
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by Seamus Heaney (found in the preface to "Statistical Rethinking" by Richard McElreath)

Masons, when they start upon a building,
Are careful to test out the scaffolding;

Make sure that planks won’t slip at busy points,
Secure all ladders, tighten bolted joints.

And yet all this comes down when the job’s done
Showing off walls of sure and solid stone.

So if, my dear, there sometimes seem to be
Old bridges breaking between you and me

Never fear. We may let the scaffolds fall
Confident that we have built our wall.