Somehow it became fashionable among site admins to set it up so that accessing over HTTP was immediately redirected to https://. But doing that adds new ways to fail, such as certificate expired:
Notice that Firefox provides no way to ignore the problem and access the website (which was supposed to be accessible over HTTP to begin with). Solution? Use Chrome, which does:
Or, disable NTP and change your PC's clock two days back (be careful with running make while doing so).
This was discussed by CKS previously (of course), and he seems to think that the benefits outweigh the downsides of an occasional fuck-up, like the only website in the world that has the information that I want right now is suddenly unavailable with no recourse.
UPDATE: Chris dicussed the problem some more and brought up other examples, such as outdated KVM appliances that use obsolete ciphers.
One thing I'm wondering about is if a redirect from http:// to https:// makes a lot of sense. If you do not support access by plain HTTP, why not return ECONNREFUSED? I'm sure it's an extremely naiive idea.