Why was the pearl harbor attack such a shock to the us

The U.S. stayed away from inclusion in WWII before December 1941 in light of the fact that the Congress and the President needed to trust that the war did not influence the U.S. This was called "noninterference" - the possibility that a nation could detach itself from others. 
The Reason
President Franklin Roosevelt was in his third term as President when the Japanese assaulted the U.S. army installation at Pearl Harbor, Hawaii, on Dec. 7, 1941. The U.S. was quite recently leaving the monetary downturn that Americans call "The Great Depression" - a period when a huge number of individuals were unemployed, lost their homes, lost their organizations, lost their reserve funds, or some blend of these challenges. 
The Great Depression kept going from 1929 to 1939. Individuals regularly abandoned sustenance. Amid this decade, outrageous climate destroyed products and slaughtered domesticated animals, exacerbating individuals' lives even. Families once in a while alternated eating or resting on the grounds that there was insufficient nourishment for everybody, or enough sheet material for everybody to rest in the meantime. 
Due to this long stretch of harsh circumstances, many individuals' lives were scarred. They were frightful and anxious without bounds. 
President Roosevelt and his counselors outlined a program called The New Deal to give business, sustenance, and plan to individuals and end The Great Depression. Many individuals looked for some kind of employment in government programs that fabricated streets, campgrounds, national stop structures, libraries, and different activities amid the 1930s. 
As a result of the Great Depression, Americans saw the activities of Adolph Hitler in Europe as horrible, yet far away. Many trusted that what Hitler was doing would not influence the U.S. in view of its geographic position between two seas. Americans thought they were protected from European wars. Be that as it may, they weren't right. 
A portion of the noninterventionists in Congress were influential to the point that they prevented America from regarding the understanding it had with Poland to help protect Poland on the off chance that she were assaulted. This is the reason the U.S. did nothing when Hitler's armed force attacked Poland on Sept. 1, 1939. The Poles asked for help, yet none came. 
Since America felt sheltered and resistant, a significant number of its pioneers disregarded the military development that was additionally happening in Japan while Hitler was working up the military of Germany. Some of their convictions were because of racial bias against Japanese and Chinese individuals. 
A couple of Americans attempted to tell the President and Congress that the Japanese had the ability to assault Hawaii and the territory of the U.S., however these individuals were overlooked until Dec. 7, 1941. That is the reason the assault was such a stun.

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Basically the usa was neutral in the war so they didn't expect an attack from japan, or anyone for that matter. *fun fact: japan actually attacked the usa to make sure they would stay neutral, which didn't work*

The growth of the empire continued to increase their confidence.