It is always better to speak the truth because if you are consistent with this policy, others will be afraid of you. This is because if your heart is pure, persons with impure mind find it difficult to hide their bad deeds and thoughts.
For example, G.R.Viswanath, the former cricket player when he was the captain of a match played between India and England (MCC) asked Taylor, who was given out by the umpire, to play saying the umpire erred in his judgment.Many people laughed at Viswanath for being so honest. In that match Taylor hit a century and India lost the match and the failure was attributed to Viswanath's generosity. But fourteen year's later, Wisden cricket club recalling this match and spirit of fair play award was conferred on G.R.Viswanath. His honesty was rewarded after 14 years. Ultimately truth alone trimphs. "satyameva Jayate"
The reason for advocating this is the firm belief in the fact that no matter how hard hearted or success driven we become, the core of a man always remains same. Hypocritical hankering for materialistic comforts may give temporary happiness but if we achieve something by using unfair means our conscience is always blames us.