He was completely blindsided, rather than not at all, and so shocked he isolated himself.

https://answers.yahoo.com/question/index?qid=20080112053013A...

> It was one thing for Stalin to begin trusting, to some extent, the judgment of Zhukov and Timoshenko (instead of Voroshilov & Co.) on how best to defend the USSR in the event of a German attack. It was quite another matter for Stalin to begin believing that a German attack would actually be launched.

> Several other answers have stressed Stalin’s refusal to accept the validity of intelligence reports re Barbarossa from Sorge and other spies. That is perfectly true. In fact, according to at least two books (‘Russia’s War’ by Overy; and ‘Third Reich’ by Burleigh), Russian Intelligence received no less than 84 different warnings of Barbarossa, from a variety of sources. Quite apart from British/American warnings (obtained via Enigma intercepts), Sorge, and various diplomatic listening posts; Moscow was being kept well informed by moles inside three German ministries: Economics, Air and Foreign. As the clock ticked down, the warnings became increasingly precise and accurate. It did not matter. Stalin kept on dismissing every warning as an “English provocation!” ... with the ominous footnote that the loyalty of the source should be investigated.

[..]

> Even after Barbarossa was launched, Stalin still refused to believe that Hitler could have ordered it. When Zhukov met him at the Kremlin late on June 22, 1941, Stalin was still insisting that the attack was “a provocation of the German officers” and that “Hitler surely does not know about it”. Once the truth finally sank in, it is hardly surprising that Stalin slunk off into isolation. Quite understandably, he feared that his staggering, glaring display of incompetence would mean the end of him. When Molotov led a deputation from the Politburo to winkle him out from his dacha on June 30, and talk him into coming back to the Kremlin to take charge, Stalin’s initial reaction to their arrival reveals that he assumed they had come to arrest him.

> This still does not answer the key question: why did Stalin trust Hitler’s intentions?

> As Churchill later wrote, at least as regards Hitler and Barbarossa, Stalin showed himself to be “the most completely outwitted bungler of the Second World War”. But ... there are a couple of rationalizations to explain Stalin’s apparently blind stupidity. To any logical man, Hitler’s decision to launch a two-front war - while Britain was still far from being conquered in the West – was crazy. Furthermore, the timing of Barbarossa was also wrong: Stalin knew that, by late June, the Germans were not likely to have time to crush the Red Army completely before the autumn rains made Russia’s roads into impassable bogs.

> However, I think that the likeliest explanation of Stalin’s obstinate trust in Hitler lies more in his Marxist convictions, and to his intense suspicion of Britain’s intentions, than anything else. Stalin did not see Nazism as being as much a natural enemy to Communism as was Capitalist Democracy. Above all, Stalin hated and distrusted the British. He constantly harked back to the 19th century Crimean War and ‘Great Game’ struggles for mastery of Central Asia, and to Britain’s post-WW1 interventions in the Russian Civil War. He was convinced that Britain was conspiring to undermine his pact with Hitler, and to form an alliance with the Axis powers to attack Russia. When Rudolf Hess flew to Britain in May 1941, Stalin interpreted it as the prelude to a secret Anglo-German pact to combine against the Soviet Union.

> Perhaps the most revealing clue lies in one of Stalin’s immediate reactions once he accepted the reality of the Barbarossa attack. He warned his cronies to expect, as a follow-up blow, an amphibious assault by Britain’s Royal Navy against Leningrad!