Last year, I was flying from Bergen, Norway (BGO) to ZRH, and I was supposed to firstly make a domestic connection through OSL. BGO is a pretty small airport, so domestic and international connections all share a single security area. You're supposed to turn left after security for domestic flights, right for international.
Needless to say, I stupidly turned the wrong way, and made myself comfortable outside my gate (or, so I thought. And no airline lounges available in BGO!). I was starting to wonder why on earth my flight wasn't boarding yet, when I suddenly heard them paging me on the PA system...
Very costly rookie-level mistake which I shouldn't have made - and I had actually used that airport before. That was the only time in my life that I've missed a flight, and I'm going to make sure that it REMAINS the only time! 
