Like when someone misspells radical candor in the second sentence of a blog post about mentoring.
Seriously though, everybody makes mistakes but when I do slip up like this I don't expect people to engage with what I'm writing. And I do think proof reading is an incredibly important skill for new and experienced software engineers.
[edit] I just noticed the author is a staff engineer at MongoDB. He can misspell whatever he wants. I recant my sassiness.