You cannot predict the future
Wouldn't it be awesome if we could predict the future? We could perfectly play the stock market, we would know if we would pass a test in school, and we would know what the weather would be like tomorrow. Somehow we haven't yet managed to figure this out. Why not?
You can't be too specific. Take, for example, the weather. It would be great if we could predict exactly what the weather would be like tomorrow, next week, next year. The most useful prediction of weather would be a personalized weather plan, based on where we would be, at what time, and therefore whether or not we need to bring an umbrella with us. Yet, we cannot predict what the temperature in a specific city will be just 24 hours from now with 100% accuracy. This happens despite having detailed weather pattern data going back over 100 years, fancy weather maps with lots of colors, and weather people that have a degree in meteorology. Perhaps we're getting better and more accurate over time, but right now, one of the problems with predicting the weather is that we all want the weather forecast to be correct for us, just one person among billions of people on the planet. If you look at weather over a much wider area, such as the midwest United States, you can much more accurately predict scenarios such as, "Will it rain in the plains states tomorrow?" but you can't necessarily predict much more specific details such as, "How many inches of rain will fall?"
Some things don't happen like clockwork. As much as we might want to be able to know exactly when the cable guy is going to show up at our house, so we can arrange to be home during the 30 minutes that he will actualy be there, some things just don't happen like clockwork. Some might say that the cable guy should be able to look at his list of visits for the day and be able to tell you, "I'll be there at 2:35pm." However, in a world where the reason the cable guy is visiting is well known, but the cause of the trouble could be any of a hundred things, it's much harder to predict precisely how long each visit will take, what traffic conditions will be like, and what will actually be required to repair each of the issues he will work on before he comes to your house. Due to many factors that are simply outside the control of the cable guy, he just can't give you a down-to-the-minute estimate of when he will be in a particular place.
Many problems are more complex than we realize. Ever been late getting somewhere, even though you left with plenty of time? Was there traffic along the way? Did you get lost? Was there construction happening along your route that you didn't know about ahead of time? There are tons of factors to consider in many "predict the future" problems, many of which simply aren't within our control. Construction is an especially good example, because not only is it unpredictable how, exactly, it will alter your travel time, the construction process itself includes tons of little details, people, schedules, etc. that are themselves unpredictable. It's much easier to say, "Will this road be finished this year?" then it is to say, "Will the concrete for the sidewalks arrive at 3:05pm as scheduled?"
There is randomness in the universe. Some of the processes in the universe act on randomness. Flipping a coin is a perfect, but simple, example. If you flip a coin one hundred times, you're almost certain the get fifty "heads" and fifty "tails". That part of it is predictable. What isn't predictable, however, is predicting what the next coin flip will be; heads or tails? You might get it right 50% of the time, but that doesn't really do you any good, does it? Events that happen with true randomness can only be analyzed to give a person the odds that a particular outcome will happen next, but not what will actually happen next. It's what makes betting work in Las Vegas.