I have never taken any pens, but as an ex- keeper, I have taken in a fair old number.
. Only saved half a dozen or so mostly by luck. I had to run out to pick one up after the poor guy had scuffed it! all the others were misses either wide, post, bar or over the top.
I will agree that penalty taking is a bit of a lottery. I have seen good takers fluff it on big occasions. It's all down to pressure or nerves. If you're cool, chances are you will score. Lack of concentration and you balls it up!