People often exhibit the effect to a great degree when referencing it, but if one reflects, The Dunning Kruger Effect does explain much human behavior...
I'd never seen that Dunning-Kruger Club graph before, it's a keeper, thanks for posting it.
I've always thought that one of life's hardest lessons occurs when we passionately believe in something.
Believe in it so much we'd stake our life on it without hesitation.
Only to discover later that we were mistaken.
It happens all the time for various reasons. Often because we have believed the opinions of other misinformed people and then incorporated those opinions into our world view until we believed them to be own trusted opinions. Politics, advertisements, different religions, selective and biased reporting from media and from our acquaintances and family all make us believe things which are verifiably false under any reasonable independent analysis.
The only funny thing about the situation is that it is so easy to spot these self-delusional tendencies in others, but not always so easy to recognize it in ourselves.
JP