When I last did a serious job search a few years ago, I thought I was pretty hot stuff. Nonetheless, I spent a few months reviewing algorithm text books and practicing code interview problems.

Then my first phone interview came, and I totally bombed it. And the next one. And the one after that. All in all, I think I bombed about seven code interviews (didn't even make it to an onsite) before I started to get some traction. One of the interviewers outright told me that I wasn't a very good coder.

After that I managed to get a couple of decent offers, but the process was quite humbling. If I interviewed again today I'd probably be in the same boat. Whiteboard interviewing is definitely an acquired skill.