The conquest of Iran by Muslims may be counted of those problems not being completely investigated. One may meet many questions in the field.  One of the questions is the reason why of the early fall of Sassanid government and Iranians` confrontation with it. This study attempts to analyze this problem in a new perspective. The paper assumes that in addition to political and economic reasons, a kind of public mentality and belief on the two parties have had effects on the status and speed of the conquest. Re-reading the historical texts and using an analytico-descriptive method, the paper intends to reconstruct the mental attitudes of those involved in the conquest, although more attention has been paid to the Iranian part. It is shown that how metaphysical beliefs have generated more or less motivations in this event.