presumably they glance at the other 90 too, and they then do a thorough verification on that random 10 the analogy is not great, but in cryptography something

presumably they glance at the other 90 too, and they then do a thorough verification on that random 10 the analogy is not great, but in cryptography something similar is at play (easy to get/check trivial properties and then hard to achieve/produce/fake the interesting ones)