I must admire your dedication, Quizzical! I too want to keep my success rate in 100 percent, which is why I was very disappointed that one time I didn't notice I'd accidentally loaded a double before it was too late.
I'm pretty sure the one day doubles occured several times within a short period was due to me using touchpad instead of my mouse (I was ill and just took my laptop in bed and didn't have any proper surface to put mouse on). Apparently the touchpad somehow interpreted my clicks as double clicks every now and then. Now that I've been using mouse again, the doubles occur much less frequently.