Full Idea
It is already a great and necessary proof of cleverness or insight to know what one should reasonably ask.
Gist of Idea
Cleverness is shown in knowing what can reasonably be asked
Source
Immanuel Kant (Critique of Pure Reason [1781], B082/A58)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.197
A Reaction
I admire the asking of unreasonable questions. They stretch the imagination, and the fixing of the limits of human thought requires some attempt to go beyond the limit. Kant sounds wise but conservative.