When the Bible says that something is going to happen, it is because it is going to happen. God is all knowing. Since God is eternal and able to exist outside of time, He can see the beginning from the end. Everything that happens in this world is like rerun to the Lord since He sees all things and knows all things. Thus, when God makes certain predictions or prophecies through His Word, its not like a human prediction. When people make predictions, there is a strong likelihood for error. However, with God, the exact things that He says will come to pass. With God's predictions, its never a matter of "if" they will come true, but when they will be fulfilled.
For example, in Genesis chapter 17, Abraham pleaded for his son Ishmael to be blessed since God communicated that Isaac would be the heir to His promises. Abraham felt bad for his oldest son and didn't want him to be completely cast away. Therefore, God promised Abraham that Ishmael would be blessed too. God would provide for Ishmael and take care of him and bless him in a different way than Isaac. God predicted that Ishmael would have 12 sons so that he would become a father of 12 tribal nations. Also, in Genesis chapter 16, Hagar sought to run away from Sarah because the two women were not getting along on account of Hagar's pregnancy and the jealousy that stemmed from Sarah. Upon conversing with the Angel of the Lord, Hagar learned that the Lord would take care of her son, but that her son would be wild. God predicted that Ishmael would be against everyone and that he would be at odds with all his brothers, mainly Isaac.
By the time the scriptures progress to Genesis 25:12-18, the Bible documents the family records of Ishmael and provides a quick snapshot of his living circumstances. Genesis 25:12-18 shows that Ishmael had 12 sons just like God predicted decades before. The Bible lists each of Ishmael's sons in order to verify his family and provide the historically verified fulfillment of God's promises and God's predictions. Genesis 25:12-18 also explains that Ishmael lived 137 years, but that while he was alive, he lived in opposition to all of his brother, just like the scriptures had predicted. It is interesting to see that God predicted Ishmael would be wild and in opposition with brothers that weren't born yet, even while Ishmael was not born yet. Then the Bible shows that Ishmael lived for 137 years, holding a grudge for his circumstances in jealousy. Ishmael allowed the bitterness of his circumstances to dominate his life so that he taught his 12 children the same bitterness, and history shows that the families of Ishmael and Isaac have been at odds ever since - just like the Bible predicted.
Though the testimony of Ishmael is brief in the scriptures, God demonstrates His power and ability to know all things through the narrative that is provided about him. There are people all over the world today who get paid to project "forecasts" and make "bold predictions," and most of them are almost never correct. Most of these forecasts and predictions are about trivial things or matter that are relatively close in time. The Bible shows that God was able to predict the birth of many people, and then describe the temperament and personality and relationship dynamics between those people over the course of decades! This is not the first instance in the Bible where God was able to accurately prophesy. In just a few chapters of the first book in the Bible, the Word has shown God speaking prophecy after prophecy, and speaking with 100% accuracy every single time. Thus, if God's Word is always fulfilled, and the matters that He predicts always come to pass, what is to stop His predictions concerning our future from coming to pass? If God has been right for the last 7,000 years, what makes one think that God will suddenly be wrong now? Even the current events in the Middle East involving Israel were prophesied to happen 3,000-4,000 years ago! The Bible is true, and the documented events in history that verify the fulfillment of God's Word prove it to be so. Know the Word. Know the things that God spoke of concerning the future, and then respond accordingly to ensure that you are on the favorable side of God's prophetic Word.