You can have too much of a good thing.
Big fleas have little fleas upon their back to bite 'em Link to proverb.
Beware the Ides of March Link to proverb.
When in Rome, do as the Romans do Link to proverb.
A little learning is a dangerous thing Link to proverb.
All the world loves a lover.
The apple never falls far from the tree Link to proverb.