The Japanese attack on Pearl Harbor is considered a military blunder because it got the Japanese into a war that they could not win. In addition, it can be seen as a blunder because it did not sufficiently destroy the US fleet.
The Japanese were not able to destroy the American aircraft carriers during the Pearl Harbor raid because the carriers were out at sea. The Japancese did not account for this possibility in their planning. Because the carriers were not destroyed, and because aircraft carriers were to become the most important type of ship in the war, the attack was not successful enough. The attack, of course, got Japan into a war with the US. The US had too much industrial might for Japan. Between the fact that that carriers were not sunk and the fact that the US had so much industrial capability, Japan was doomed to lose after in attacked Pearl Harbor.