Often in the comments on questions involving challenging sums or integrals, I will see someone make a comment something to the effect of "Do you have any reason to believe this has a nice answer?" I'm curious as to what sort of assurance the user making such a comment is looking for. If the problem is something like a homework problem and the answer is already known, it would certainly be helpful to indicate that in the question.
In other cases where it is not already known that a "nice answer" exists, it is often not obvious (at least for me) that a problem has a "nice answer" until an approach to finding that nice answer has been found and the problem is basically already done. In a question like this, what other sort of a priori evidence of "niceness" is being requested?