Let's put it that way, even if i know you're going to commit a crime i can stop you or not right?
Even if i know that there is a cliff in front of you and that you can fall there, i simply can keep quiet, or warn you and yet you will go straight there by your own will.
God knows exactly what would happen when He created man, He also knows exactly who is the vessel of honor and who is not. Instead of utterly destroying the human race, He sent His son so that the righteous would be justified by the sacrifice of His blood, consequently being saved by His acceptance.
Jesus died and rose again to save us all from the eternal damnation(lake of fire) that would be given only to satan and his angels. After the God's judgment, only those who are not written in the book of life(salvation) will be thrown there. In a few words, those who know the word of God and the right, but nevertheless chose sin(here we return to Adam again, because this is the nature of the human being by inheritance).
Be assured that there are people who think they are saved but will be condemned, and people who live wrong but will achieve redemption. Perseverance in God's faith and the acceptance of Him in the spirit and truth are the key to salvation, not simply doing good deeds as many churches erroneously preach out there.
The subject is complex and difficult to understand for those who don't believe, but more than this only the Most High can tell you