Idioms for competing demands

Are there any popular idioms in English meaning that one cannot always possess and take care of two precious things (say, family and enterprise,romance and reality) together?
Thanks a lot!

These may not be exactly what you require, but they're close.

You can't have your cake and eat it.

or

A dog cannot have two masters.

I thought that was "A man cannot serve two masters"?

An idiom used when too many projects or concerns are taking up someone's time and attention is "spreading oneself thin."