For instance, if you have a problem, and someone says "The answer to your problem is the set of numbers 1, 2, 3, 4, 5", a computer may be able, quickly, to figure out if the answer is right or wrong, but it may take a very long time for the computer to actually come up with "1, 2, 3, 4, 5" on its own. Another example includes finding prime numbers. It is easy to check if a number is prime, but it is very difficult to find those numbers in the first place. For some interesting, practical questions of this kind, we lack any way to find an answer quickly, but if we are provided an answer, it is possible to check—that is, to verify—the answer quickly. In this way, NP problems may be thought of as being like riddles: it may be hard to come up with the answer to a riddle, but once one hears the answer, the answer seems obvious. In this comparison (analogy), the basic question is: are riddles really as hard as we think they are, or are we missing something?