The Revisional Commissioner is expected show that the view taken by the AO is wholly unsustainable in law before embarking upon exercise of revisionary powers. The revisional powers cannot be exercised for directing a fuller inquiry to merely find out if the earlier view taken is erroneous particularly when a view was already taken after inquiry. If such course of action as interpreted by the Revisional Commissioner in the light of the Explanation 2 is permitted, Revisional Commissioner can possibly find fault with each and every assessment order without himself making any inquiry or verification and without establishing that assessment order is not sustainable in law. This would inevitably mean that every order of the lower authority would thus become susceptible to Section 263 of the Act and, in turn, will cause serious unintended hardship to the tax payer concerned for no fault on his part. Apparently, this is not intended by the Explanation. Howsoever wide the scope of Explanation 2(a) may be, its limits are implicit in it. It is only in a very gross case of inadequacy in inquiry or where inquiry is per se mandated on the basis of record available before the AO and such inquiry was not conducted, the revisional power so conferred can be exercised to invalidate the action of AO