The shock may be brief, but the memory can last a LONG time. When our #2 son went in for his shots before entering Kindergarten, he asked specifically which shots he'd have to have in future years for school. The nurse was amused, but told him he wouldn't have to have any more before 7th grade. When she gave him the shot, she just walked up to him, and jabbed him in his leg. He screamed bloody murder right in her face. She was shocked (duh?), and looked at me like I was supposed to rebuke him or something. It was all I could do NOT to say, you deserved it, you hag!
All the way home, through his sniffles, he said how glad he was that it was 7 years before he had to have any more shots like that. As the years went on, he'd remind me of the incident and let me know how much time he had before the next one. When 7th grade came around, he was nervous, but got a sweet nurse that time, so it wasn't as traumatic!