The truth of believing essential. matter cannot be known by any believer directly and the doubt on possibility of falsehood remains always in him. But we decide to accept it as truth and believe it. What makes us believe? We have many reasons why we believe. 1) When the saying seems to be truth, we believe it. This seeming can be gotten by the coherence of saying or its rationality. The evidence to stop the doubt or the repetition of honest behaviors can help to believe. 2) Every belief or trust includes its own risk and has some promising merits. If we have a guarantee for the contract, we can diminish the risk and easily trust it. On the contrary when we find the increase of merit as the large profit or gain which may be gotten by the trust, we also can facilitate the trust. 3) Among family or friends we have the affective trusts which are supported with the coincidence of interests and shared identity. Generally with this coincidence or identity we can increase the trust. 4) The sanction against a lie and the reward for truth also serves to increase the reliability of saying. When sanction threatens the person who masquerades as a trusty but wants to tell a lie, he fears to tell a lie and in consequence we can believe him. Reward for truth accelerates the trustworthy saying. 5) The competence and sincerity of person is important for reliability. Sincere person is ashamed of lying and a man of competence can achieve his promise undoubtedly. Hence we can trust him. 6) Finally the subjective factors of individual believers must be considered. Concerning the same believing matter one can believe it and the other cannot with theirpeculiar subjective reasons. Innocence is more credulous than average. Sometimes greedy man also may easily trust for his greedy mind.