Having a bad day
There are times where nothing you can do is going to work out right. You do your best and it's just not good enough. You think everything is going alright and suddenly you realize your fifty steps behind.
And then there are the times when you try to improvise and the result is a dud. I won't share the embarrassing details, but the short version of the story is that I tried to fly by the seat of my pants on something that required a lot more attention to detail then I gave it and I didn't get anywhere close to my standards.
However, the embarrassing part is that I know the reason behind my sub-standard performance. I've lost my focus on the job at hand. I just don't care. I want and need to be doing something else.
In all, I've just had a very bad day and I only have myself to blame.