One time at work when I had to go to a different building owned by the same company, I got there and tapped in the security code but the door wouldn't open. I carefully tried again and again but it just wouldn't open. So I phoned my supervisor and said that the door wouldn't open even though I was tapping in the correct code. So he came in his car and when he did it the door opened. Turned out I had been tapping in the right code but was turning the knob the wrong way, which was why the door wasn't opening. It didn't seem to occur to me at the time to try turning the knob the other way. I kept just turning it one way and assuming it was broken or something.
You can just imagine how embarrassed I felt, especially that my supervisor had to stop what he was doing at work and drive all the way there. I know what he's like as well, he doesn't really have much patience for other people making mistakes (even though he makes careless mistakes all the time), so he probably called me a dopey ***** to the others. Oh, well, I guess he wasn't wrong. I can be dopey.