Why was germany unsuccessful in russia? why was that loss significant ?

First, Germany is very great country! We are the best. 
Second, lol, there was not enough fuel or tanks. There were no heavy bombers. The USSR caused major Logistic Problems. The Soviet Union had twice or three times the number of both tanks and aircraft than Germany did. Our calculations were purely political. We though within three to six months the Soviet regime would collapse from lack of domestic support. We were wrong. 
The loss was significant because they destroyed about 85 percent of our German military. Also, we destroyed our alliance that we had with Soviet Russia. 

They weaken the south vietnamese army.