What leads you to believe the events described in the preface of I Know Why the Caged Bird Sings are painful to recall?
The preface of this incredible autobiography focuses on a highly embarrassing childhood memory of Maya Angelou's when she trips up in church and wets herself. Note how Maya responds to this tremendous indignity:
So I ran down into the yard and let it go. I ran, peeing and crying, not toward the toilet out back but to our house. I'd get a whipping for it, to be sure, and the nasty children would have something new to tease me about.
Clearly, reliving such an embarrassing and painful childhood memory is not going to be easy to recall. However, more importantly than this is the way that Maya as a child is shown to dream of being white and how she hopes one day she can "wake out of her black ugly dream" with her "real" blonde hair and blue eyes. The painful nature of this sense of dislocation is captured in the final two paragraphs of the preface:
If growing up is painful for the Southern Black girl, being aware of her displacement is the rust on the razor that threatens the throat.
It is an unnecessary insult.
The strong words used and the comparison of the awareness of displacement to the rust on the razor combines images of violence and pain with the childhood that Maya experienced, making it clear that what she narrates is painful.