Ouch, I missed last week's post. But I think the countermeasure should be easy.
The problem has to do with my adoption of the tickler file, one of the great great great elements of the GTD methodology.
You use a folder per day, and in each folder you put notes. I used to have a note saying something like "Did you write the blog post this week?", which I placed in the folder for the upcoming Sunday. That way, I was sure I had a checkpoint for my weekly post if I wasn't able to get to it before Sunday.
The problem came when I started writing down in other papers some ideas for future posts. Those papers went into the folders too, but their function was not clearly enough defined: finding them means "write this post", or just "remember that you have a blog?". In the middle of that confusion, I must have lost/decided to throw away the original checkpoint note.
So the countermeasure is: creating a new checkpoint note for Sundays, and taking the papers with post ideas out of the tickler. They are not warning signals, and I don't need to overload my mind with them reading them before I'm ready to act upon them.