Today’s lesson of colloquial expression
619. to write the book on something 熟知している
- this means that somebody is very knowledgeable about something (so much so that they could write a book!) and is usually used in the past tense
1. John wrote the book on poker, so if you’re wanting to learn about it you should talk to him.
2. I don’t need anyone to teach me what to do…I wrote the book on what I’m doing!