Why Marxism doesn't work

Watching This video makes me realize just how unrealistic Marxism is.  Its not that Marxist are bad people, I fully believe that they truly have the people's best interests at heart, particularly poor people.  However, the Marxist version of reality, in my opinion, is wrong. That's why Stalinist/Leninist Soviet Union and Maoist China ended up the way they did.  In theory Marxism is great, in reality however it could never work, and this video proves why.