She can't even chew gum and walk in a straight line, let alone write a book.

Summary

This quote highlights the speaker's belief that the person in question lacks not only basic coordination skills, but also the ability to accomplish more complex tasks. By emphasizing the inability to perform a simple action like chewing gum and walking in a straight line, the quote suggests that the person's incompetence makes the idea of them writing a book highly unlikely or impossible. Ultimately, it expresses doubt in the person's overall capabilities and casts doubt on their potential for achieving more complex endeavors.