I am an idiot

This is the title of the latest xkcd, which you really need to read to understand the rest of this blog, and I am highly ashamed to report I've done exactly the same thing. 

I was locked out of work, I got in through the front door with my key, but the keypad into the section of the building where our office is was jammed. I decided to call the people inside to let me in but my mobile phone battery was dead. I wandered round the corner and called them from a payphone and got let in.

Of course, I could just have gone outside the main front door and pressed the doorbell. D'oh!