Once bitten, twice shy

“Once bitten, twice shy.”
Is it a standard proverb in English?
What does it mean?
Where or in which situation is it used?

It is a well-known saying.

idioms.thefreedictionary.com/Onc … +twice+shy

‘‘Look, if push comes to shove we’ll have to change the reforms’’.

What does it mean?

idioms.thefreedictionary.com/if+ … s+to+shove