Why did one injection hurt and others didn't

I had a similar experience. I never had an epidural before.  I remember the Dr. saying we are getting close to the nerve.  That hurt a lot and I said something like don't do that again.  She said something like, that means we are getting close. Then pain exploded, searing pain from my back down my leg. I screamed, and told her to take it out.  She said something like, are you sure.  I screamed, I think, at her to get it out.  She took out the needle and I was pretty much in shock, on the table for the next few minutes as the agonizing pain slowly subsided.  Sweating, etc.   Later on, after I could get up, she met with me told me that if I could not tolerate that pain, then I was not a candidate for most other pain intervention options.  After reading many of these posts, it appears that this level of pain is a rarity in epidural injections.  I am still researching, looking for posts from doctors providing an explanation.  My hypothesis, however, is that this only occurs if the needle actually punctures into the nerve, aka, medical error in locating the needle near, not in, the nerve.   

Hi, I had my injection into my spine yesterday, I can withstand a lot of pain, but this was out of this world !!! The pain went across my lower back and went straight down both legs, it was excruciating. For a few minutes after I couldn't move. I will NEVER be having that done again. But today I do have to say that I am pain free for the first time in a long time, so what ever it was they did, it has worked.