Probability of Success

Probability of success is the Achievement of the war's purpose must have a resonable chance of success. The United States anticipated the Vietnam War as being a quick "in and out" type of war.  They were very confident with their army strength, and they thought they were superior to the Vietnamese.  The probability of winning this war was particularly high.  But, the war was not even close to be considered an "in and out" type of war.  This war lasted 16 years, and ironically it was the longest war for the United States.