For example: Judas. He had the opportunity to not] betray Jesus. But he didn't choose that. We know that now. God and Christ knew it then. He still had an option before him. He chose unwisely.
I like to use this analogy:
Say that I'm your math tutor. I am your only instructor and you are my only student. One day, I prepare a test for you to take. I hand a copy of it to you and you begin on the test. While I am waiting for you to finish, I take a fresh copy of the test and amuse myself by filling in the answers how I think you will. I know what you know and what you don't, so I know exactly how you will attempt to solve each problem. Not only do I know which questions you will miss, but I know how you will screw up. I happen to finish the test before you, so I go ahead and grade my copy of the test. You got an 87. I mark it in red pen and put the test face down on my desk and decide to go home for the night. I tell you, before I leave, that you can look at my copy of the test for your score once you finish with the test. You don't believe me, but you find that I was 100% completely correct. Did I make you fail? Did my foreknowledge of your failure somehow influence you? Is my judgement fair? Did you earn your grade all on your own?
I always like Sci-Fi movies where they say that there's one past, one present but multiple futures. What is the future but someone else's past? How could there be more than one future, then? More than one possible future maybe. But there will be only one future. Just like there is only one past. And just as someone who is in the present can know the past, someone who is more than time can know the future. Without influencing it.
Xhonzi