I know a lot of smart people.
I also know a lot of people who think they're smarter than they are (even the smart ones ... or, perhaps, especially the smart ones).
It's common. So common, in fact, that there's a name for it. The Dunning-Kruger Effect.
Have you ever met someone who's so confident about what they think that they believe they know more than an expert in a field? That's the Dunning-Kruger effect. It's defined as a cognitive bias where a lack of self-awareness prevents someone from accurately assessing their own skills. It's getting increasingly more common.
Here's a graph that shows the general path a person takes on their journey towards mastery of a subject.
via NC Soy
It can be funny or frustrating to see (or be) the "victims" of this effect in our daily lives.
Humans seem prone to overestimating their knowledge and abilities. It's probably more a result of ignorance than stupidity.
Even if you are familiar with the cognitive bias caused by the Dunning-Kruger Effect, you are not immune to it — because you don't know what you don't know.
Two different ways that people get it wrong, first is to think about other people and it’s not about me. The second is thinking that incompetent people are the most confident people in the room, that’s not necessarily true.
Usually, that shows up in our data, but they are usually less confident than the really competent people but not that much... - David Dunning
It should be a reminder to reflect inward, not cast aspersions outward.
To close out, even this article on the Dunning-Kruger effect presents a simplification of its findings. First off, the above image isn't actually a part of the paper on the Dunning-Kruger Effect (though it is ironically so prevalent that people often report that it is). Furthermore, the connection between a lack of ability and the inability to engage in meta-cognitive tasks is intuitive, but it is not the only potential takeaway from the paper. It's worth a read if you have the time.
Regardless, I think it's clear we are all victims of an amalgam of different cognitive biases.
We judge ourselves situationally, and assume "the best" of ourselves. Meanwhile, we often assume "the worst" of others.
We can do better ... it starts with awareness.
Progress starts by telling the truth.
