Sent my application and got the first interview. However there were 2 months between when I sent the application and got the first of 2 interviews. In that time I had booked and paid for 3 weeks of vacation.
I went for the interviews, and told about my vacation, which meant I could not start immediately as I wrote in the application. My soon to be boss said that should not be a problem - great.

Next day I got an email saying that they went with another candidate.

I called the now x-boss an asked what had happened. He told I submitted my application twice, and that was the reason I did not get the job.

True. I did sent my application twice, but only because I made a mistake when typing in my email the first time.

Apparently that was a huge mistake.