"You only notice when something is missing because you have lend it."what does the narrator mean?bring out the sarcasm in her comment

The narrator took no notice of her mother's items when they were in her own house. She only started to notice the things that were missing, after they had been taken away by Mrs. Dorling. ​The narrator says this sentence to explain how we underestimate the value of something and take it for granted and only notice its absence when we do not have it. The comment can be considered to be sarcastic because, she has lost both, her mother and her mother’s items due to the war. Just as she felt the absence of her mother’s items as a child, she feels the absence of her mother as an adult.