Some problems are undecidable: no computer can solve them, no matter how powerful.
Think of an impossible puzzle: you want to know if a program will ever get stuck, but you can't find out for sure. Turing showed there are questions computers can never answer, even if they are very fast. It's like trying to find a treasure that doesn't exist.
Suppose you write a program that checks if another program will crash. Turing proved that such a universal checker cannot exist. This means that no matter how smart you are, you cannot build a machine that predicts all crashes. It is like trying to create a complete list of all possible lies. In everyday life, this explains why your antivirus sometimes misses new threats.
Why it matters This limit of computation helps us understand why some problems, like perfect security, are impossible.