Witnessing a milestone turns the simple into the profound. To see the look on your child's face when they've realized that they have toes, or fingers or that there is a cat in the house makes me appreciate that I was present and watching (and writing!).
Things that I wrote down in our baby memory book:
"At Christmas held a rattle at Dr's office with a look like 'Oh, I didn't know I could do that." 3 months old
"First notice of the cat, like 'Wow, I didn't know we had a cat.' She pointed and squealed." 7 months old
"The first time she sounded out a word and she got it." 5 years old