to be something that you know or understand nothing about.

I'm afraid physics will always be a closed book to me. (usually + to)

• love something to bits
• love to bits
• love to death
• low ebb
• low-end
• lower guard
• lower sights
• lower the boom
• lower the tone
• lower your guard
• lower your sights
• lowest common denominator
• lowest of the low
• low-key
• low life
• low man on the totem pole
• low on the totem pole
• luck into
• center on someone
• center on something
• C'est la vie.
• chalk something up to
• chalk something up to something else
• chalk up
• chalk up something