Rawls's Thought Experiment - Should Everyone Get Equal Liberty?

In a thought experiment, Rawls asks people to choose between two principles. One is that everyone gets an equality of liberty; the other is that those at the bottom should have enough. But there are interesting objections to both: who made this pie? And does it matter if you're born with incredible athletic ability or can compete in Wimbledon and make lots of money because of your own luck?