Why do I always know after the fact what could have been better?

Why do I always know after the fact what could have been better? I swear this has been happening so much and I just can't seem to break the cycle. I keep going into the same pitfalls. I had 3 chances the other day to say something better and the same result happened all 3 times. Okay, so I was out the other day at an optical place to get an adjustment for my glasses. I sat down with the optometrist and explained where I was having pain. In this explanation I stuttered but nothing really bad. On a couple "L" words, my tongue got stuck but besides that no big deal. Then the optometrist asked everyone's favorite question, "What is your name?" I started off fine: "My name is ..........and nothing. Completely blocked. Eventually pushed through the block and said it. She made the adjustment and told me to come back if I still felt pain. After I left I thought to myself "I could have said my name better so next time I'm going to ease up on the tension." So I was still in pain and came back for another adjustment. This time another person had been working. I explained the situation and she asked the same question: "What is your name?" I didn't listen to my own advice at all. I panicked and blocked again. No easing up on tension whatsoever. So she made the adjustment and once again tells me to come back if I still feel pain. At this point I've made 2 attempts to do it right and struck out both times. I said to myself, "For this 3rd time I am going to exhale, take a breath, pace myself, and start gently and slowly." So of course I still had pain (these doctors can't do anything right lol) and here it was, here was my moment to finally get it right. The popular question was asked once more. The minute she gets done asking the question, I immediately start to answer and it results in a block. I didn't pace myself, I didn't exhale, I didn't do it gently. I just tried to speak and this is what happened. Block after block after block all 3 times but my intentions were good. I knew what to do and when the moment struck, still couldn't do it. I even practiced it in the mirror beforehand but the moment I'm in front of somebody, that practice doesn't mean jack shit. I just don't get it. I know what I need to do to say my name clearly but when the opportunity comes, I'm unable to do it. Why?