Everyone deserves a SECOND chance. not third, fourth, fifth or sixth. If they don't get it right the second time they'll never change
It's saying only forever give them once cause if you do it again then they will continue to go on and do it...
I think its pretty clear, it means when you give someone another chance to prove themselves and they still fail then they would never change.
It means someone might make a mistake once, so they should be given another chance. But if they keep on making the same mistake, it means they're doing it intentionally and not learning from their past mistakes (i.e. in other words, they don't care)