Some things are just harder on me than on the girls

Today Hayley had her 2 month old check up. Hayley weighed in at 13 pounds and 23 1/4 inches tall. The Dr. told me she has amazing head control, which should come at 3-4 months. We are thrilled. The worst part of going to the Dr.'s is the shots. Hayley got 3 shots and 1 oral med. She took them like a champ. She cried when the needle was in her leg but as soon as it was out she stopped. Mom on the other hand was teary from the time it started until I got to pick her up again, I was like this with Aubree as well. Hayley's legs are a little tender but with the help of some Tylenol she is sleeping and being her sweet self.
Why are somethings so hard for parents, its like this instant protection you feel for them the moment you give birth.