Cold fusion is supposed to be impossible because the energies of chemical and nuclear reactions differ by several orders of magnitude. Ron Maimon here provides a history of cold fusion's rejection and even a theory to explain how the process could work.
wait it blew a hole in the floor?!
the hell? I thought we were talking about tiny amounts of energy in the systems that were experimenting with.
Information that surprises you is interesting as it exposes where you have been miscalibrated, and allows you to correct for that.
I suspect the users of LessWrong have fairly similar beliefs, so it is probable that information that has surprised you would surprise others here, so it would be useful for them if you shared them.
Example: In a discussion with a friend recently I realised I had massively miscalibrated on the percentage of the UK population who shared my beliefs on certain subjects, in general the population was far more conservative than I had expected.
In retrospect I was assuming my own personal experience was more representative than it was, even when attempting to correct for that.