1. (1) When the author left home for the first time, her mother also missed her very much and worried about her (it is human nature and easy to understand). At this time, it was especially easy to receive missive messages from her daughter. Cause triggering.
(2) This is the first and only birthday card the author personally made for his mother.
2. The author just made a crude birthday card for his mother, and even forgot about it afterwards, but his mother kept it in the most precious place, together with those solemn documents. It can be seen how easily mothers are satisfied and moved.