Peter Thiel on Secrets

> Secrets are unpopular or unconventional truths.

Merriam Webster's first definition of a secret is "something kept hidden or unexplained," emphasis mine[1]. Secrets are not usually unknowns, but things purposefully hidden or not shared. I don't see how unpopular or unconventional has anything to do with secrets either. Those features will be dependent on the information in question.

He immediately equates something unknown with something purposefully hidden. That seems like paranoia to me, which would explain some of his behavior.

[1] https://www.merriam-webster.com/dictionary/noun