We are deeply intuitively familiar with our everyday physical world, so it was perhaps a bit of a surprise when researchers discovered a blind spot in our intuitive physical reasoning: it seems humans are oddly terrible at judging knot strength.
One example is the reef knot (top) vs. the grief knot (bottom). One is considerably stronger than the other.What does this mean, exactly? According to researchers, people were consistently unable to tell when presented with different knots in simple applications and asked which knot was stronger or weaker. This failure isn’t because people couldn’t see the knots clearly, either. Each knot’s structure and topology was made abundantly clear (participants were able to match knots to their schematics accurately) so it’s not a failure to grasp the knot’s structure, it’s just judging a knot’s relative strength that seems to float around in some kind of blind spot.
Check out the research paper for all the details on how things were conducted; it really does seem that a clear understanding of a knot’s structure does not translate to being able to easily intuit which knot will fail first, even when the difference is a considerable one. There’s a video demonstration and an online version of the experiments if you’d like to try your hand at it.
It’s always interesting to discover more about our own blind spots, in part because exploiting them can result in nifty and delightful sensory illusions. We wonder if robots are any better with knots than humans?