How does the author use metaphor in the memoir, The Tender Bar?

When Moehringer was young, he was deeply attached to a security blanket past the time Dorothy felt was healthy. She began to snip slivers off the blanket, making it smaller until it was no longer useful to Moehringer. This was a literal blanket, but it became a metaphor for all the other strong attachments Moehringer formed, often in unhealthy ways or for unhealthy reasons. His relationship with Sidney was one example, but the more obvious was his dependence on the bar.