Explained by Bryan Caplan:

George Stigler famously observed, “If you never miss a plane, you’re spending too much time at the airport.”  I heard that he wasn’t amused by his secretary’s corollary,  “If you never make a typo, you’re typing too slow.”  But he should have been.  And I’m very amused to see Robin Hanson get in touch with his inner Stigler:

Look, in any area where we let humans do things, every once in a while there will be a big screwup; that is the sort of creatures humans are. And if you won’t decrease regulation without a screwup but will increase it with a screwup, then you have a regulation ratchet: it only moves one way. So if you don’t think a long period without a big disaster calls for weaker regulations, but you do think a particular big disaster calls for stronger regulation, well then you might as well just strengthen regulations lots more right now, even without a disaster. Because that is where your regulation ratchet is heading.

Link can be found here.