An anecdote of mine (details obscured to protect the innocent):

A friend of mine (who is okay with me sharing this) came down with a debilitating illness. He scheduled an appointment with the doctor, and attempted to diagnose himself using the Internet. During his visit with the doctor, the doctor agreed with his self-diagnosis, but demonstrated lack of knowledge regarding major findings about the relevant illness that had occurred in the last 10 years.

Deciding doctors were useless, my friend proceeded to treat himself using advice from the Internet. It wasn't until many (pain filled) months had passed that my friend realized he exhibited additional symptoms that weren't adequately explained by his self-diagnosis, and began to rethink his treatment.

This could potentially demonstrate positive bias in my friend's failure to look for disconfirming evidence for his self-diagnosis, his failure to properly understand unknown unknowns and visit more doctors, and maybe some form of priming when my friend's misdiagnosis helped his doctor fail too.

Of course, this is probably too much detail for the homepage, but the anecdote could possibly be slimmed down.