If you can quickly check an answer, can you always quickly find it?
Some problems are easy to verify but seem brutally hard to solve — like finding a short route through a huge map of cities, versus just checking whether a given route is short enough. Computer scientists call the 'quickly checkable' problems NP and the 'quickly solvable' ones P. Whether P actually equals NP is one of the seven Millennium Prize Problems.
Reveal the answer
Nobody knows. It remains unsolved, with a $1 million prize from the Clay Mathematics Institute still unclaimed since 2000. Most computer scientists suspect P does not equal NP — that some problems are genuinely harder to solve than to check — but no one has proven it either way, and a huge amount of modern cryptography quietly depends on that suspicion being true.
— Clay Mathematics Institute, P versus NP problem — Millennium Prize Problems, posed 2000