I've been reviewing knots, and this problem occurred to me:
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(if you already know the sheet bend, never mind)Can you tie this knot, first try? Study the diagram. Grab two ropes. Start as shown - form a loop with the left rope. Easy peazy, I expect everyone here will succeed.
Next, the challenge: Grip the two ends, one in each hand. Now tie the knot, directly, like a shoelace, WITHOUT forming the loop.
Can you nail it, first try? Harder than it looks! Spatial visualization is a valuable skill for any engineer -