That happened to me w/ the first SYD-LAX flight a few years ago. I thought I'd beat the crowd and get to SYD before hand and then ride the inaugural SYD-LAX. I flew ATL-ICN and was awaiting KE ICN-SYD when I decided to take another look at the SYD-LAX list.......I had gone from #3 w/ 15 seats to #20.

I ran back over to the DL gate and hopped right back on the airplane ICN-ATL.