One of the most painful interviews I have ever seen was a guy who had a resume listing a number of interesting projects. He could talk energetically and in detail about them. Then we asked him to write some code to solve a simple problem. He said he didn't know our primary language, but was very familiar with Python. I know Python, I was good with that.
He didn't know Python. I tried to help him, but he didn't get much farther. I eventually called the interview, with a complete 180 of my hiring opinion. Nice guy, but he couldn't be what we needed.