Let's say that you know an incredible one percent of all the knowledge in the universe. To know 100 percent, you would have to know everything. There wouldn't be a rock in the universe that you would not be intimately familiar with, or a grain of sand that you would not be aware of. You would know everything that has happened in history, from that which is common knowledge to the minor details of the secret love life of Napoleon's great-grandmother's black cat's fleas. You would know every hair of every head, and every thought of every heart. All history would be laid out before you, because you would be omniscient (all-knowing).
Bear in mind that one of the greatest scientists who ever lived, Thomas Edison, said, "We do not know a millionth of one percent about anything." Let me repeat: Let's say that you have an incredible one percent of all the knowledge in the universe. Would it be possible, in the ninety-nine percent of the knowledge that you haven't yet come across, that there might be ample evidence to prove the existence of God? If you are reasonable, you will be forced to admit that it is possible. Somewhere, in the knowledge you haven't yet discovered, there could be enough evidence to prove that God does exist.