Conversation so far:
What is the Principles of justice?
The first of these is the Liberty Principle.
What is the Liberty Principle?
establishes equal basic liberties for all citizens.
What is another principle?
a two-part second principle comprising Fair Equality of Opportunity and the famous (and controversial) difference principle.
Why is the difference principle controversial?
CANNOTANSWER.
What is the Fair Equality of Opportunity principle?
wherever one ends up in society, one wants life to be worth living, with enough effective freedom to pursue personal goals.

Question: What is the difference principle?
Self-contained rewrite: What is the difference principle?