It depends on the random number generator.
If you use random numbers for physical simulations, or maybe in a computer game, you don’t care whether the random numbers are predictable or not. What you care about is that you can produce different sequences, and often that you can replay a sequence. And you like one that is fast.
In cryptography, or if you run a lottery, you want numbers that are not predictable. Some random number generators have that property, some don’t. Those that cannot be predicted are called “cryptographic”.
Your average linear congruential random number generator is predictable, but it can be hard work. If I use one with 32 bit state, and give you the results of 50 simulated coin throws, and you know how I calculated the outcome, you can write a program easily that identifies the seed and predicts the next coin throws in a few minutes. If you don’t know my exact code, it is a lot harder. If I used a cryptographic RNG it would be impossible.