Was Hitler Arrogant or Just Stupid to Think He Could Defeat the Soviets?

The greatest martial mistake Hiter did was attacking the Soviets in the Second World War, however, I never understood why he thought that was a good idea. Was he just arrogant, and believed that the German Army was superior to the Soviets? Or did he believe that the Soviets would retreat deep in Siberia they wouldn't be a threat? I've always been confused by his decision to attack the Soviets.
Thank you.


I didn't find the right solution from the internet.
References:
http://hi storum.com/european-history/127403-hitler-arrogant-just-stupid-think-he-could-defeat-soviets.html
POS Solution Video